probably to make this feeling that this coin is still cheap to make people buy it.
Price has to do with supply and higher supply can also equates to cheaper price. So yeah. There are still people that look for other factors before they invest apart from the price. This is how proper investing would be. Apart from what you said there, a high-supply coin might also be easy to manipulate. If the devs has a bad intention, they will usually prioritize it.
but truth to be told, there are investors and traders who trade based on the coin price, which is ridiculous, but I guess this kind of gimmick still works.
We can't deny that price is also important, especially for the traders. Every count or movement matters a lot to them. If they are skilled enough, yes it is possible for them to profit even if they only invest in a cheap coin that has a huge amount of supply. Usually they are only doing it for the short term to cut the risk.