It comes from a dogmatic reaction against microservices. Microservices were problematic in certain ways, but instead of analysing what went wrong and why, they just went the opposite direction and started doing "big services only". It was a misguided approach, plain and simple.

Interestingly due to internal bureaucracy and understaffing in some teams, there was a lot of "multiple-teams-per-service", which yeah, is another issue in itself.