I don't think trainers of any kind are available on Tibiantis are they?
There are no designated trainers on Dura, but it is relatively easy to find yourself an appropriate self-healing troll/dwarf to train on - this makes training significantly easier but doesn't remove the danger or directly prop up the online count.
For these old school servers, having training requiring significant "down-time" is part of forging the social aspect of the game. For Tibiantis, paladins and knights probably require a mage friend to summon and train with - the mage is probably making runes to feed the economy too.
For Dura, knights and paladins can also make useful runes themselves, and in doing so they feed the economy too. In both games, the time allows for social interaction which for many is a very big part of the game for them.
Training (and I include rune sitting as part of this) isn't part of what you might describe as "fun gameplay" in relation to other MMO's - It isn't fighting, questing, raiding, fast, exciting, blah, blah - but it is part of the element that made Tibia so engaging to start with.
None of this applies to servers that have vast training monk areas where you can just sit and safely afk or even exit log. Generally I agree with what you're saying for those servers.