Because it trivialises the weight of the original choice.
E.g. consider marriage. If you knew you could only divorce for a massive cost would it change the way you pick a partner Vs. If divorce was instant, for free and a new partner selection was guaranteed? Would you also invest the same amount of time in either case?
Answer honestly
That's a pretty bad analogy, in fact, if you wanted to use such an example, not having a respec option would be more akin to not having the option to divorce your partner. Divorces are pretty common because people make mistakes and sometimes things turn out different than you thought they would, so if you're unhappy with your marriage, you get a divorce. It gets ridiculous when you put it like this, the people arguing against respec are people that are happily married, that don't want other couples to be able to divorce even if they're unhappy, and that apparently couldn't stop themselves from going for a divorce even when they claim they are happy in their marriage, just because that option exists.
Yikes.
If you don't want to respec your character, just don't do it, it is not a mechanic the game pushes you to interact with, if you can't prevent yourself from doing something you don't want to, that's a you problem.
The analogy was about stating more choice being always better is not necessarily true.
Argument being if marriage was extremely easy to break the partner choice wouldn't be so important and the decision wouldn't matter as much.
In retrospect I think you can push the envelope of this analogy even further: if you have been married or/and committed in a relationship for a long time (e.g. 10/20 years) you will know that you have modified your behaviour somewhat (I don't believe in that case where you partner just take you 100% like you are and let you carry on without affecting your life, unless it is a goldfish).
You commit, you adapt, you try to make it work and you reap the reward in the end.
I see a parallel here: free or almost free respec would I think encourage a sense of laziness in carrying on with whatever playstyle routine until you stumble on the combination fitting your playstyle. Costly respec would force player adapting to the choice they made in order to make the most of it, ultimately making them hopefully discover new playstyle.
Imo one elegant way to solve this problem would be to jack up the respecing cost to 4-5k in tactician and scaling up with the level because, sure, nee players and non DND player will make mistake and will need a respec mechanism but advanced players picking harder difficulties should benefit from being challenged
