Why does upvoting a post takes 3 seconds?

Because light travels at a certain speed.
It is a blockchain, and every transaction on it must be confirmed and added to a block. That takes some computation.

Why 5 minutes break between 2 posts?

Not aware of this.
I think the new limit since hf 20 is 3 seconds.

20 second lag between comments?

Just got changed; it's also 3 seconds now.

Masses are used to lightning fast activity on Instagram and Facebook.

Those fast platforms are centralized.
For some applications that's much better and results in a better user experience.

On Steemit however, you have a different type of security, guaranteed immutability, personal, signed transactions.

On facebook everything gets stored in one big database ( on server clusters with backups, I assume ).
If a facebook admin ( or a hacker ) wanted to change your posts, he could.
Nobody could tell, who changed the data and what the data was before ( perhaps after going through the backup servers, it is possible, but those can get changed/ hacked, too ).

On Steemit, everything you have ever written will be stored forever.

There are upsides and downsides to blockchain technology.
Depending on what you want to do, Steem might just be the right place.

Have you made any money on the other platforms ?
Is your vote worth something on other platforms ?

Btw, glad you finally post some text.
I had voted plenty of your photos in the past, but was not so sure, if you appreciate it at all.