[konart]

Main reasons:

1) Telegram Channels has channels among other features. This is like streaming rss feeds right to your IM. Channels quickly became a most useful thing for media that is opposed to the regime or just shares the information that would be censored otherwise

2) Telegram has no censorship, the do not block those channels either

3) Their security might not be perfect, but it was enough for the said media to deliver information withough being caught in any way. Some of the media actually switched to Telegram Channels completely.

All of this (and some other minor things) goes agains the will of the regime obviously.

Not being able to see or hear what people say about you is on thing, they can deal with this like they did years ago. But they can't stand the fact that they can't controll the flow of systematized information.