It is not just TVC-MAS. It is also for QLN, CGNR, KTYM, ALLP, ERS/ERN, TCR, PGT and all the intermediate stations, all of Kerala south of TCR. For all these there are only 3 daily (GNWL) trains. And Mail is RLWL north of ERN (AFK, TCR, PGT).
CBE alone has got 2 daily overnighters and 2 day trains. For the others too, number of seats are not really meager. The daily MAS Superfast has got 130 Sleeper berths for Coimbatore in PQWL.