I suspect they were done for good reasons, but they irk me.
They encourage you to take a group of related skills for a discount. . .but if your character concept already has you buying a related group of skills you don't get a discount if it's not a group of skills covered by an existing TP.
So perhaps it encourages power gamers with their eye on the costs to pick up skills for the discount they'd never bother with, making them more rounded, but that's what many gamers do regardless, create realistic, rounded characters. . .it's sort of like bribing munchkins.
To that end, I find that munchkins just turn around and game them anyway to min/max ahead. Especially the ranking limits, how often have you seen a character who took serial packages that give OB or spells without caring at all what all the other skills were? So getting way over the top ranks in one skill is the whole goal, and their character accidentally forms from the pastiche of odds and ends in the TPs associated with the one or two skills the character wanted.
There are a lot of TPs, but it's not exhaustive, and in the end, at least for me, it's bribing people to round out, but only from among a limited set, which leads to "It pays to create a rounded beleivable character, but only if you use our building blocks, if you create a rounded beleivable concept on your own, you pay full price." which feels kind of railroady to me. . .and create your own TPs can lead to a mess. . . if you tailor make a TP for each level of each character, then why not just drop the costs of all skills by a fixed percentage?