I know I've told this story here before, but I'll tell it again. In Bentley's first agility class we worked with target plates. The exercise went like this: show the dog that you put a dollop of peanut butter on a target plate. Show him, get him excited about it, etc. Then, hold him back while you place the plate a few feet in front of him. Then, release him to the peanut butter! Bentley would just stand there. It's not that he doesn't like peanut butter, but he thought that since I had pulled him away/not allowed him to have the peanut butter, that he shouldn't have it. So he refused to try and get it. I thought our agility career was over before it started!
Bentley now has his ADCH, and while he isn't the fastest dog out there, he definitely isn't the slowest either, and I believe that he does enjoy the sport.
There are some dogs that have more drive than others. My 3 dogs are living proof of this. But, I think that every dog can be taught to be MORE drivey if done in the right way.
The first thing that I did was sit down and think about what Bentley loved. He doesn't like toys at all, but you know what he did like? He loves to chase my husband and I in the yard. He would bounce around barking and smiling the whole time. So we incorporated chasing into agility. Instead of a food or toy reward, he would get to chase me at the end of a run. He also gets excited if you push him around (not too rough, of course!) so we worked on that. Before each exercise, he and I played together.
While I'm not a devout Susan Garrett follower, she has a great philosophy about working with your dog. You need to be the most fun thing out there. Find something that your dog finds irresistible. It's different for every dog. For example, for Bentley it's my husband and I

, for Lexi it's getting the chance to keep playing, for Enzo it's toys. We also struggled to find treats that Enzo cared a lot about, and finally found a homemade meatball recipe that he ADORES. Other treats are enh for him. So when we first started he'd rather circle over to one side, or check something else out unless we had a toy or a meatball.
The one thing that is a little separate from drive that I want to mention is stress. Sometimes sniffing is just "hey so many yummy smells I'll be over in a minute", and sometimes it's avoidance and stress. It's hard to say without seeing each dog which you're experiencing. If it's stress, find things that make Simba comfortable. What is his default behavior? When Lexi is stressed outside of agility, I get really yummy treats and we just work on sits and releases. She loves to sit haha! So much so that she does it and looks at me sometimes because it's her default. So when I ask her to sit, reward and release it builds up her confidence. "Yes! I can do this! Yes! Cookies!" and her stress diminishes. For Enzo, it's tugging on a toy. If you can't find something that eases your dog's stress in the ring, you might want to take a step back. Can you work farther from the ring? Can you stand in the doorway and do fun things? Can you go to the training building on other nights and just watch? Don't ask Simba to do anything except have fun with you (toys, treats, pets, etc.) then go home.
To answer your specific question about the exercise where you were supposed to throw a treat, I will say that if Simba loves to tug than I am confident that you can get him to tug/retrieve. When you tug, how do you get him to take the toy? If you haven't already, start using a verbal with this. We use "get it!" So if I'm holding the toy and offering it to Enzo, I'll say "get it!" and he gets very excited and grabs it and we start the tugging game. Also, start moving the tug toy around on the ground. Keep it in your hand, but move it around and then use your "get it" command when he gets excited. Keep tugging with the toy low. Do this a lot. Build up excitement and drive for that moving toy on the ground. When he is confidently and excitedly going for that moving toy, move it around and then tell him to "get it" and let go. As soon as he picks it up, grab the end and tug. You don't even want him to notice that you let go. Do this for a bit, and slowly add two things: 1) space between you and the dropped (eventually thrown) toy 2) time/space between you tugging with him. For the first bit you'll be just letting go of the toy right in front of you and picking it up to tug immediately. The next step is to let it go maybe 6" in front of you, and then grabbing it with him and tugging. Next, try not grabbing to tug it right away. Wait a second, then tug. Or stay excited and engaged and step back maybe a step, encouraging him all the way.
The last thing to mention is that it can be really tiresome, but it's super important with a dog with sightly lower drive to always stay excited and engaged. It goes back to making yourself more fun than anything else. I once had a trainer say that it was harder to run a lower drive dog because you have to be "on" all the time. Act like everything you do, and everything they do is the most fun ever! Celebrate even the tiniest victories. If other people are throwing the treat 6 feet out and their dogs are running to get it excitedly, throw your treat 6 inches out and party when Simba gets it. Cheer and reward and play and act like an idiot. Honestly, it's fun!