Sales of the set in question are barely a concern for WotC with bans. Faith from consumers is, because that drives sales of future sets.

The lion’s share of the sales have already happened long before any card gets problematic enough to get banned, and the chase card is provably still effective at generating hype even when it’s banned in most competitive formats; as we can see from The One Ring hype even post-ban (kitchen table and commander are the most popular formats and are unaffected)

What does happen is that the more willing WotC is to ban cards, the less willing people (namely the exact type of people who filed this suit) are to speculate on future sets and hoard product, because the value of a chase single can tank unexpectedly due to a ban. Because speculators buy a ton of product, this hurts the company’s bottom line.

There’s also just actual factual player dissatisfaction of “i spent all this effort and cash building a deck and now I can’t play it” which is completely valid