There is however a reason why the more expensive DAW's have their price.
Mostly that they have more overhead and are actually in it to make a profit.
Justification to buy at those higher prices comes down mostly to more bundled ready-to-play instruments and sometimes third party plugins that you'd otherwise have to buy separately. It may be true that you can save a little bit of money on the bundle prices compared to buying Reaper and the same or similar plugs, but that's only a value if you actually want/need those plugs.
I have not yet found a professional studio that uses Reaper as it's main software. Why? Who knows.
Either you're not looking hard enough or you've got a very narrow definition of what a "professional" studio actually is. I get paid to record/mix other people, and use Reaper exclusively, so now you've found one.
Over on the Reaper forum we hear from people using Reaper to make money all the time. We're there helping some of them make the transition from whatever they were using before.
But the "industry" as a whole does tend to be pretty conservative and both studio owners and their customers can have a sort of brand fetish. People I think expect to see ProTools because it's been marketed as the "industry standard" for so long. It has name recognition and is what "all the pros" use. Heck, it says "Pro" right in the name!
It's also true that people equate price to quality in a way that just doesn't apply. Reaper has the disadvantage that anything else in it's price range is just a toy, so people don't take it seriously.
When you're advertising a studio, you sometimes have to pander to your customers expectations even if those expectations are a bit misguided. Two studios with the same gear list, one uses ProTools and one uses Reaper. Anybody who "takes themselves seriously" is booking the one with PT. Sad but true.