With the skyrocketing of Doge coin as a Meme coin, many developers started creating theirs hence the reason many where created with even more supply you can imagine, well according to some people it is easier to pump. But however, we need no one to tell or explain to us what a shitcoin is and what it's not, anyone trying to paint a better picture of what shitcoins is all about is probably trying to shill or hype the project to people.
Also, whether large supply or not, there have been many projects with less supply which are still shitcoins, so in a way, shitcoins is not only about coins with very high supply but coins with no use case, no tangible thing from the team other than shilling in different social media channels and so on.
A coin like SOL doesn't needs shilling or hype from the team, what it offers and what the team are capable of doing is enough to create the right hype.