ChatGPT is nowhere near being able to replace search, and even if it was remotely similar, many people don't even really know what it is, whereas Google is ubiquitous with search.
To say they only have a lock on Gmail is doing them a huge disservice. They own a huge part of online advertising and search.
For Gmail if you mean a lock on consumers who generally don't pay for the product I would agree, but I have done more g-suite to Office 365 in the past 12 months than I have in the past 5 years. It is too bad because we could really use some competition and different ideas in the office productivity space.