You have made a number of classical "Western" mistakes.
Firstly you speak of the Taliban as a singular tight entity, whereas in fact they are no more than a collection of loosely knit 'tribals' with a common goal,... and that is to gain independence on a national and individual level, the way they are going to do this, is to rid Afghanistan of foreign influence and steer it down the fundamentalist Muslim path, and the only reason they use Islam is because it is the one singular thing that all the tribes and sub groups have in common. Fundamentalist Islam is not the actual goal, the goal is power, but to acheive power they know they must unite their supporters.
Secondly, you talk of the Taliban as "ruling" the tribes, whereas in fact they are not rulers but appeasers, who play to the tribal mindset promising them (and giving them where necessary) what they want, thereby winning their support.
In Afghanistan you don't "rule" the people, you gather their support, and the group with the most support gets the most say,... which I suppose makes it a true democracy
The Taliban will only be supported any tribe, group or individual, so long as it is advantageous for that tribe, group or individual. The instant that Taliban (or anyone else) is seen to interfere that group's interests, they will turn on them too,... but of course, the Taliban being comprised of "tribals" themselves fully understand the mentality of their fellow countrymen and will go to almost any length to see that this does not happen.