IME we had multiple services for each team. But we were in the process of carving several mutually incompatible whales into common, shared services, YMMV. So we had one team maintaining each whale, and our senior engineers would collaborate to identify pieces that could be cut from each and replaced with a common service. If the innards of one whale matched our service better than the others, that whale's team got to write the service. Eventually all the teams would port their products to the new, resulting service.

This meant, for example, that my team, had our whale, an audio transcoding service, an automated transcription service, a post-phone-call messaging service, and several data integrations.

If you need a whole team to do nothing but maintain a service, it seems to me like you built it to do too much.