A lot of it is about opportunity cost. Do you take someone fresh out of school or someone who's been around the block a few times if the latter costs only 50% more? The cost of even a junior but basically able programmer can be quite high if their work has to be redone (heck the cost of a non-junior but bad programmer can be high), so you end up needing to assign tasks that aren't that important or for which large slips can be tolerated. It can be tough to find a supply of such tasks sufficient to keep people fully throttled.
There is no difference between senior wanting to change things
Seniors are more likely to have been through several jobs and environments, and learned that tooling choices aren't that big a deal at the end of the day. They've also already (hopefully) got some accomplishments under their belt and don't need to redo other people's work to have something to show - they're more likely to do higher risk strategies like trying new things as a consequence.
There is no difference between senior wanting to change things
Seniors are more likely to have been through several jobs and environments, and learned that tooling choices aren't that big a deal at the end of the day. They've also already (hopefully) got some accomplishments under their belt and don't need to redo other people's work to have something to show - they're more likely to do higher risk strategies like trying new things as a consequence.