Why low Tier waystones in end game maps?

Did my first Tier 15 map, had a tough map that gave me 670% Waystone drop rate. I had 1 Tier 4 and two Tier 5 waystones drop in the entire map....

Not only did I feel that this was abysmal for 670%, but also felt that having these tier maps drop in a Tier 15 map was insulting.

Like I just killed the big boss and he only had pocket change and a coupon for 60 cents off a cheeseburger on him...can't get a good mugging these days.

I took screenshots but would need to upload them somewhere if we are using URL. It was corrupted, +1 level and the only real positive I had were 9% increased quantity and 14% increased rarity. I myself have around 150% increased rarity. Maybe I am missing something, but I feel like I have routinely seen maps drop that are several tiers below the map I am doing.

For towers i guess , you dont wanna burn juiced maps for towers. Just use one worst and put your tablet.

Lowest-tier waystones can drop anywhere and yes, it's bullshit. They could get this somehow right with skill gems, why not with waystones, too?