Servers cost money to upkeep. So owners of big instances could start posting, ads, pin them and ban other users posting ads or delete their posts. This is obviously almost the worst case scenario. I feel that it wouldn't happen in the near future, as Lemmy grows to become a larger platform.
I haven't seen this type of ads on Reddit so is there something stopping this?
Advertisements aren't coming to Lemmy. It's never going to happen. Why is everyone talking about it like it's inevitable. If you think that's going to happen, you haven't been in communities like this enough.