Because you reach 10-1000 times as many people. As one can also see in the picture of the post (well, you don’t see the number of views, but it’s likely in the same range as likes and comments are).
It sucks and I hate reddit. But how else can you reach the people that are not on the fediverse?
Your tech level is more than sufficient. Just follow the install instructions on the official site.
Tuta is alright. One of many good alternatives. Just try it out in parallel.