This is not accurate; it depends on the subfield. As a rule, the more theoretical the subfield, the more likely that alphabetical order is used. See e.g. papers from a theoretical conference like STOC vs. a systems conference like HotOS.

If you look at the papers of the third author [1], almost all of them seem to be alphabetical by last name.

[1] https://arxiv.org/search/cs?searchtype=author&query=Kuszmaul...

Interesting! I didn't realize it varied between sub-disciplines of CS, I guess.

Theoretical computer science and cryptography both typically do alphabetical. Maybe because of their adjacency to pure math?