2.4GHz routers with 300Mbps but more than 2 antennas? Any clue?

Tenda F3
3 antennas
2x2:2 (wikidevi)

Xiaomi Router 4c
4 antennas
2x2:2 (wikidevi)

There are more of this devices but lets focus on the 2.4 band.

Why do they have more than 2 antennas? What are these antennas for?

Just like Linsys WRT1900AC series, there are 4 antennas but only 3 of them are used for tx

Same thing as the big, fat antennas currently in vogue, marketing.

In some cases, it may just be reuse of existing case design. Cheaper to flop a cheap board into an existing case than design another.

Total crap specifications defined.

It is a 10/100mbps ethernet device but specs says... Max. LAN Data Rate: 300Mbps.

It even goes to mention 802.11a when it is just 2.4Ghz.

Total misrepresentation.

Could 2 antennas be used for trasmit?
And 2 antennas for recieve?