The TS6M was designed and built for 1 purpose -- Slalom skiing. Your post is basically saying, "Why do people like Corvettes so much? I bought one to haul firewood and it sucks at it! Plus it doesn't fit my in-laws and it's hard to get in and out of because it's so low!"
Ridiculous.
The TS6M is a great handling boat and was the first of a new generation of purpose built slalom boats.
If it's not something that you like, feel free to sell it.
Now if you're asking why some of us others like their older Supras, I bet you'll get a lot of different answers. Why do I love mine? I built it myself and customized/set it up for exactly what I use it for and what I need. It's got a great surf wake, a decent wakeboard wake, lots of room, lots of power, is easy to work on, looks great and serves all my purposes from party-coving to relaxing and drinking a gin and tonic while the sun sets to making a mean wakesurf wake.
Former owner of a 1987 Supra Saltare. Current owner of a Malibu 23LSV.