Reaching over 100% crit rating makes people uncomfortable for good reason, because it's purely wasted stats.
I can't think of the maths right now, being that it's 1:30am, but it's similar to an inverse of the probability of seeing an item drop. For example a mount that has 3% drop rate always has a 3% chance to drop, but the probability of you seeing said mount in X number of kills increases each time you kill the boss. (Better explained
here).
Imagine it coming from the other end of the spectrum. If you have 80% crit, getting up to 90% from that point is less valuable than going for a different stat. It would change you from getting 8 out of 10 spells as crits into getting 9/10 spells as crits, but what if you had that 10% worth of stats placed into say, mastery, which would increase the damage of all 8 of those crits, and both of the 2 non-crits instead, rather than just buffing 1 of the spells from a non-crit into a crit. The higher your crit gets, the less valuable it becomes. Once you get above 100% crit, you're wasting stats, because you're already getting 10/10 spells as crits, anything higher than that doesn't somehow magically make you get 11/10 spells as crits, because that's not possible.
Plus, the amount of time you sit near 100% crit is so minimal, it doesn't mean that your incinerates are giving double the ember regen that they normally would, it works out to a far lower AVERAGE amount of crit, which is what you would base the number of embers gained off of.