Which is your choice, obviously, but you can see why people would find it strange -- it seems like you're potentially just leaving value on the table for an arbitrary reason. The price of Fastmail doesn't affect the value you would get from some unrelated product, so surely that other product is either worth the asking price or not worth it regardless of how much Fastmail is charging.

What do you mean infinite vendor lock in? Just export your vault and import it in another password manager and switching email provider is not that hard either (assuming you use your own domain).