That's not entirely true. The difficulty depends on what someone wants to do on the platform. No one is asking for the ability to write an essay or anything like that.
It's simply to access content that's not available because there are no apps for it. There have been plenty of situations where apps are denied to be in the App store because content/company is censored for various reasons.
Furthermore, my understanding is that there is a basic type browser for Roku tech that's not accessible to the public as someone pointed out that the privacy policy is displayed using it.
On some Google TV, a mouse key feature is included to navigate using the arrow navigation around for clicking. It's not too hard to use.
Also there are many mini keyboards separate from and included with remotes that can be useful. Here are a few examples from Amazon that's pretty inexpensive for those who wants to be able to type a bit more.
The bottom line is pretty clear that ROKU doesn't want to make this available for whatever their reasons. As I've shared, my reasons are pretty straight forward: to keep my set up simple without additional hardware to support, more cost having to get another device when the TV is very capable, access content not accessible with the current available apps, and environmental--with more devices means more electricity, etc.