To answer your original question, OP... A lot of people in the UK did the equivalent of GSCE French at school. Their French may be atrocious, but they could at least have a stab at pronouncing the name of somewhere in France. So deciding to rebrand a French location with a French name wouldn't cause as much head-scratching.
How many people in the UK speak Welsh? Particularly outside of Wales? I'm not even going to ask how many outside of the UK speak Welsh.
The issue with 'renaming' something in Welsh is that no one will know how to pronounce it. And no one wants to sound like a twat. "Where are you going on holiday?" "Oh, I'm off to <mumbles>." "Sorry, didn't catch that." "<mumbles even more sheepishly>"
It also implies that it's for local people. Which is fine, but it's an odd choice if it's a tourist attraction and you want tourists to come to visit and spend money.
I think it would be different if it had always been known by its Welsh name - it then becomes a case of respecting local culture and tradition rather than trying to 'change' something to make it less welcoming.
Doesn't bother me. I'm not the hillwalking type, so I'm unlikely to ever visit anyway, regardless of what it's called.