As you said, TAESA started as a very promising carrier, having the newest fleet in Mexico. No older DC-9s or 727s, only new 737s and 757s/767s. It instantly became Mexico's 3rd major airline. This was in the early 90's. But as the years passed, TAESA's problem became evident, and it didn't take long for people to realize something was very wrong with this airline. What is this problem? Well, something that pretty much reflects a problem of Mexico itself: corruption. TAESA began with its well known extremely poor maintenance standards,
insufficient crew for the planes they had, etc. TAESA's directors did whatever they could think of so they could earn extra bucks for themselves, and they just didn't care if this meant poor safety for passengers and crew. That's why they eventually replaced their great fleet in favor of second-hand, old, cheap aircraft. Well, the fact is, NOBODY was surprised when they knew about the DC-9 crash. It's very common to hear "I think an accident like this had to happen to them sooner or later."
I could mention several other things about TAESA's terrible administration, but I think I've made that point clear. In my opinion, it's sad that the airline wasn't shut down until an accident that killed 18 people took place...
"... for there you have been and there you will long to return."