Project outreach, to keep spreading the word through screenshots etc. This is a free projects with no marketing, to the logo is a sort of branding.

It’s the (very small) price you pay for a great and free product (I think it’s great!!!). If you don’t like that ‘feature’ you’re not forced to use it ;-)

you mean the tab bar...?

Gee, I wonder why that's there.

Also there is an option, modify the libre source code that is provided to you.