Maybe partially for security. If somebody broke in and removed channels, you may forget what channels you had, and then they lose money.
I don't understand this problem. I once had added too many channels and did not have enough memory in my Roku box so I had to delete some to get Roku to work. I followed the below instructions which I got from Google by asking How to remove channels from my Roku box. This did work perfectly.....I did have to use the newer Roku remote with the asterisk button on it as my old Roku box remote did not have that feature.
"Go to the Home Screen, select a channel you want to remove and press the * button on your remote. then. Select "Remove channel" and press "OK" on your remote to remove that channel from your Roku. Repeat this procedure for any additional channels you'd like to remove."
Hope this helps.
It would be nice to be able to remove channels online, my folks just ran into this problem when they set up an account for my 1st gen Roku that i gave them, they added some channels online but some didn't install because they weren't compatible with the older Roku, so there's no way to remove them from their account, they're not on the Roku itself so they can't uninstall from there and of course they can't uninstall online. Which actually brings up something else, they said that some of the channels showed as incompatible when they tried to install, but obviously others didn't and showed as installed even though they weren't.