To hit different price points.  Not everyone can afford an $850 ski boot.  So we do our best to downgrade the boot, but take super care not to "cheapen" it.  In fact, if you look at what you get with our ski boots vs. other competitors on the same price point, we will 99% of the time have more/better features. It ultimately comes down to this at the end of the day: when the end consumer wants to spend less money, they will get less.  That goes for cars, bikes, TVs, houses, boats, shoes, etc.
But to a point I think you were making/alluding to, I think there are different ways that products can be downgraded.  The tricky thing is that the boot market has a "barometer" in place and it's hard to go against it.  I totally agree with you that some people want a 100 flex boot with the best liner (usually found in a 130) but so few people (in the grand scheme of buying ski boots) would pay top dollar for a 100 flex boot.  The big problem is that so much of the boot market places value on a flex number.  So if Atomic has a 100 flex boot with a premium liner but Competitor-X offers a 120 flex boot with a lesser liner for the same price, the market buys more of Competitor-X instead of Atomic.  It can be frustrating at times, believe me.