Do people follow certain mazhabs just because it is simply what their previous generation have done? Do they follow not because there is mentioned of benefits found in the Quran and authentic hadith but merely as a way to preserve their identity considering what mazhab could define them?
The different madhhabs spread in different places largely due to historical accidents. Many Maliki scholars ended up in North Africa and Spain, so these places become firmly Maliki to the present day. People follow the madhhab that is followed by most of the scholars and imams around them.
Things are changing nowadays due to the increase in communication between different parts of the Islamic world so that madhhabs are becoming less relevant. Check out the following answer on how Muslims today can follow Islam beyond the madhhabs: On deciding which madhhab to follow and the multi-madhhab approach