They instruct financial institutions world wide to cease processing transactions to/from telegram and freeze their accounts or lose access to the US banking system and risk having their assets frozen.
it's not a huge investment, and does not cost any money; market share really doesn't matter here when you can get in easily. you also can download the app on their website without installing their store app.
also keep in mind that telegram definitely can distribute their app on their website, like they do with desktop apps.
That would affect hundreds of millions of people who rely on their phone apps for chat. For others, Telegram would still work with its desktop clients as well as the browser based version at web.telegram.org.
Except that the word blockchain is entirely unnecessary here. How would IPFS not suffice? Or Bittorrent? Or Telegram itself. Unless no country on earth is willing to host X, X can host somewhere. This "X" can be Telegram itself or the app store that it is on. You make blockchain sound like magic pixie dust, but what the word means is something like git (see the Wikipedia page about it for a definition), not "magic pixie dust that makes something unblockable".
