Good question!

Most of the heat doesn't go into evaporation. If it did, we wouldn't have higher temperature during the day, just more moist.

Truth is, I personally think farming evaporation is leagues more ahead of datacenters. Datacenters are more of a nuances locally, where depleting resources already don't give enough water to keep households water pressure up. Add to that a new water-hungry datacenter, and pressure in pipes drops even more.

They aren't bad on their own, but in a context where they want to share a depleting communal resource.

Edit: tl;Dr farming is worse but historically there. There is a lot of discourse around that, also, but it's a separate issue.