Ahh the Google wrangling, bringing back unpleasant memories from webdev when I kind of had to think about seo sometimes XD
If I was to tell you today my work can also be seen on platform 'x', would you, as a consumer, feel the need to go to the other platform to see the same stuff?
That's assuming that all the potential consumers have got multiple accounts on multiple sites. Some do, most don't seem to, so the logic behind cross-posting is that you'll reach different people on different sites and thus expand the audience.
I don't know how people manage that many accounts unless they're full time managing social media on top of doing whatever they're doing, or they're just not answering comments.
I also know people who use art sites as a form of cloud storage and delete all their files after uploading x_x ("they take up too much space") so if they're site monogamous and that site goes for whatever reason that's all their work just gone. So a lot of them spread it around different sites to mitigate that risk.
Please keep messing with Google XD
A problem many of these platforms face is they're filled with creators not working to attract consumers. Creators simply throwing work everywhere hoping something sticks. Many of those platforms don't have a dedicated consumer base and quite a few lack the social setting. Who's looking at the work (aside from a few followers trickling in) if majority are creators scrambling to post everywhere? If crypto is involved, there are plenty of other factors one must consider as well. I see a lot of time being wasted. It works for some though. Not many. These days we can create a market and direct traffic to it, using other platforms, rather than attempting to be in every potential market going virtually unnoticed.
Storage is fine but if everyone did that for those reasons and did nothing for consumers, those platforms have no future. More efficient ways to store files as well.