There are many reasons and purposes for those tasks, which are to reduce the circulating supply, reward holders, and donate to charity. At least that's what most of them do.
However, sale tax is like a scam already. Because firstly projects with their marketing, make their users think buying NFT, playing games will bring a lot of profit. At the end, most of promised profit will be charged through sale tax and the project team take it. What they do with those sale tax income, users can not control.
Calling tax as the name of whatever it is that they charge is suspicious to me, they could give it another name or just call it changes, because I believe that taxes goes to the governments. So if the developers of these projects call whatever they charge as tax, then they're obligated to remit it to the government, if not, then it's a scam, because you can't tax investors and withhold the taxes that they pay, it is criminality. It doesn't matter how legit an altcoin is, collecting charges from investors shouldn't be called taxes, let them find another name for it.