Sub bass can still be felt on headphone just like loudspeakers, so that's not the issue.
Headphones aren't automatically disqualified because they don't include sub-woofers.
In almost all circumstances, good loudspeakers will almost always be better than headphones.
But most of us either just love headphones or need to use them due to the following restrictions:
- size of house/room
- disturbing neighbours/family members
- poor student (money restrictions - good headphones are cheaper than 'equally' good speakers)
- need good isolation from noisy environments and can't get your own room
... I'm sure there are other reasons too.
There is a small number of absolute bass-monster headphones out there, but most people just want to upgrade to something that doesn't have the awful QUALITY of bass found in almost every cheap headphone.
Most requests are not for sub-wooferish bass-drops, but for headphones that can produce bass notes with all their tone and texture.
They do exist, and quite a few are better at it than a set of speakers at the same price point.