Define "real bass". Don't most tube integrated amps have it? At least if used in a smaller room and/or with suitable speakers?
The problem is more likely that there are relatively few speakers that can do bass really well with most tube integrated amps. Ones that can are likely very big and very expensive.
When the amp has limitations, the speaker has to take up the slack (easy load, high efficiency, etc.). That's the case with tube amps.
With SS amps its the opposite. Speakers can be smaller and less efficient, which the evidence indicates is what most people prefer.
Doesn't make one better than the other necessarily... just different "paradigms" as they say.