because people dont know how to care for their cars.
you will find same case with civics. plenty of engine changed ones.
i dont know why. its original engine is very reliable. never once gave me any problem. my own civic is now at 223,000 km. no oil consumption no smoke.
by maintenance what exactly you mean?
either you find a good car so you dont need to spend much on maintenance.
or you buy a cheap car and then just replace every thing you can with new parts. and new parts are quite easily available in karachi. again all depends on your knowledge.
for suspension i can recommend Abdul Hameed and sons (afzal bhai) at saeed manzil near plaza market. but still keep your eyes open.
for AC works i can recommend SABIR, North nazimabad near 2k stop. dont bargain dont negotiate.