I used to think that too but these days website versions are so crippled sometimes they're unusable on W10M/Edge. Constant popups saying "Hey you're on mobile, download our app! iOS/Android links here."
I could not even get mixer to work in Edge and MS don't have an app, which is dumb since Mixer is owned by them. It's starting to get annoying.
Some of it isn't MSFT's fault at all.
There are websites that will deliberately mislead people into believing that their site can't be viewed on so-and-so device or browser.
The truth is is that they can be. Just not necessarily how the web designers want people to view it, pixel for pixel, ad for ad.
Coincidentally, MSFT tends to correctly block out the most ads in my experience.
Case in point, I'm on Chrome on an Android right now and a forum ad link that I accidentally opened popped into a page which popped up with a 'Your Android device is infected' ad which is a 'download malware' scheme aimed at Android users.
If I were on my 640 right now, it wouldn't have happened - even if I clicked on that same link.
I discovered this discrepancy when I was still using UC Browser and wondering why the native web browser was having problems. I opened the same page / site using UC's ability to mask itself as a different browser and discovered that I actually -could- view it and that it was the website itself was the culprit and not my browser.
True, there were and still are sites that are problematic, but now with Edge it should be less and less.
Try desktop version like was suggested and / or make sure you're not low on phone resources.