Why?
Of course there is several reasons.
One big reason is looks and with that WAF.
As a designer it starts here:
Hoffman’s Iron Laws of Speaker Building
1) Bass Extension
2) Efficiency
3) Small Enclosure
So you can choose two and the third is given to you.
If you want more extended Bass Extension and high efficiency (sensitivity) then you will have that but you will not get that in a small enclosure!
So you need a big ugly speaker enclosure and the market is not going for that. Sorry.
If you go for high efficiency (sensitivity) and a small enclosure then the bass extension is gone. That is not HiFi if you don't can hear full range.
But there is manufacturers that makes higher sensitivity and higher ohm speakers. So it is just to look elsewhere.