One way I look at it is by the time you beat the game for the first time unless you've done quite a bit of side content, you still may not be a high enough level to unlock all of the abilities. You've only seen a fraction of the unique items floating around since most don't even drop until World Tier 3 or 4. You've likely only gotten the chance to play one or two themed builds based around the items which have dropped. You've probably not touched the paragon board or glyphs which can change things up quite significantly and enable a number of other builds that aren't really viable without the boost. I'm "only" level 78 on my main and I'm still upgrading glyphs and working my way through the paragon board. Or I was before the season started, and now I'm playing a fresh barb instead of sorc.
I wouldn't mind more free respec opportunities, but I don't think it's exceptionally expensive. Just verified on my 78 sorc that it would cost just over $1MM gold to reset all of my points. That's maybe 3-4 dungeon runs. However to reroll an attribute at the enchanter, it's now costing me above $1.5MM for a single role, it also requires forgotten souls. Refunding skill points is much cheaper than upgrading end game gear! It also took me an embarrassing amount of time to realize you don't have to reset all skill points. If you right click on a skill it'll remove it one point at a time for under $20k / point.