Groudon and Kyogre are the same way.
commented 1 minute ago by J™
Yes, they are also so the same way(Precipice blades has 10 more BP than Origin Pulse), but it's mainly for balance purposes, considering Origin Pulse is power-up in rain by 50%, so it's actually 165 BP most of the time considering its ability Drizzle, in most cases.
Calyex-Ice has the same Attack stat as Calyrex-Shadow's SpA stat so it makes entirely no sense why Glacial Lance is better than Astral Barrage in terms of base power.
Yes, that's true, but don't forget that Calyrex-Ice needs Trick Room support to be useful, and considering that most sets run Heavy Duty Boots to prevent the chip from Stealth Rocks, while Calyrex-Shadow can hold Life Orb, Choice Specs, etc. which make it better than Glacial Lance, and it can do many things without support.
Thus, we may conclude that its mostly for balance purposes.
Hope this helps!