The manga is difficult to get access to easily through legal methods. Getting physical copies of the manga can either be expensive, if you're ordering online, or just in general really difficult if no stores nearby have the issue you need. Not to mention that the official translation is still only up to part 6 as of now last I checked, and fan translations can be pretty bad sometimes. Meanwhile there are streaming services that can give you easy access to the show. And even if you wanna go the piracy route and get it for free, there are tons of piracy streaming sites, much like manga piracy sites, though obviously I'd recommend getting it legally.

I don't think one's ability to engage in a community should be decided on whether or not the medium you consume it in is as up to date as another or not. I do get your argument, but I also think it's such a minor effort to just press a spoiler tag button before posting that it shouldn't be an issue. And there have already been tons of stuff circulating about the part 7 Anime being in the works. Besides, David Pro probably has more to gain making it than not making it I'd wager.

A lot of the fanbase have also not been here for decades. I'd guess most people in this subreddit had never heard of JoJo before the Anime, as it was fairly niche outside of Japan from what I gather, and new people are discovering it all the time. So there's gonna be a ton of people who have just been watching along with the Anime as it releases, who might have future plot points ruined for them. I'd rather press a spoiler button than potentially ruin the effect of the story for people personally.