Simply because ownership is power. Power in the hands of individuals is harmless as it is mostly Brownian motion; on the other hand, power in the hands of huge corporations (or governments) can turn nasty very quickly.
This is the reason I stopped using VSCode even if the tool is very good.
Ownership is too important, with heavy long-term political consequences to be ignored or traded for short-term convenience.
Basically, anything running "in the cloud" or slowly converging to run there should be a red flag.
Without being paranoid or a luddite, you can do everything with mostly local-tech or at least diversified enough to avoid giving too much power to a single actor.