The traffic you refer to only costs reddit money and doesn’t directly make reddit money.

The real question is how much indirect money it makes. The nature of social media is that only a tiny number of users actually make content and you need that content for the other users to stick around. I think third party apps users are disproportionately the heavier users that bring this indirect value.

Plus, since reddit makes money from ads, the opinions of advertisers matters. If reddit’s brand is tainted, that makes them less appealing to advertisers and that means less money. I think it’s in reddit’s best interest to be a cherished site that people like.