Absolutely not true that this is niche. Almost all international online saas or stores have embedded translation and copy teams.
It's probable big ones like Amazon do have their own translation teams, but generally speaking most companies (in any industry) rarely hire a translator directly and work with agencies.
My wife is a translator and works for a number of agencies. I see the projects she works on, and that even includes some very large companies like Facebook or Netflix.
Poedit does not support nested yaml files, and this application supports them, and it will be useful even if it's used by single person.
So for example you have these Chinese restaurants menus with terrible translations and nobody cares if the translation is good.
What about legal texts or maybe medical brochures?