There's a sharp difference between the other examples you list (aside from perhaps Reddit) and X.
When a person posts an antisemitic on X, the people who notice said post do not know with any certainty what ISP was used, so there's nothing to associate the post with a given ISP. Furthermore, even if readers did know what ISP was used, the general assumption (correct or no) is that ISPs don't monitor traffic going through their pipes, so they neither know nor can control what data is sent over the wire, thus absolving them of any responsibility for what someone decides to post on X.
Contrast this with X itself. As the host of said message, there's a direct link between the content seen and X. As X already moderates content on its platform, a claim can be made that it bears responsibility for posts that are left up for any significant amount of time. The fact X sells ad space which appears next to the hosted content only reinforces this responsibility.
If you prefer to deal with a meatspace analogy: consider a billboard company. Should someone rent space on a billboard in a widely-visible area and paint a giant penis on it, most onlookers would disapprove, and they'd foster a growing discontent with the company the longer it's left up. However, few, if any, would attack the nearby Lowe's or Home Depot for selling paint and paint brushes that could have been used for the picture or go after the city for daring to build and maintain the roads allowing access to the billboard.
X is a digital billboard company. They aren't neutral here: they're actively aiding you in getting your message in front of more people with the hope that any engagement your message triggers will increase ad revenue.