For good reason. That was probably intentional. Critical hits basically double the damage.
For most purposes you can consider a 40 BP move with 100% crit a 80 BP move with caveats.
Critical hits can miss, so even though both are reported as 100% accuracy, they are in actuality 99.7% accurate like most 100% moves.
Critical hits ignore positive defense modifiers on the target, so if they had +2 stage Defense boost from say, Iron Defense, it is ignored. I think it also hits through Reflect and Light Screen. However if the target had negative modifiers to Def or Sp.D, those are taken into account.
Similarly, crits ignore negative modifiers on Att and Sp.A, but take into account positive modifiers.
Finally, every move besides ones that state they have increased critical hit ratio hits a critical attack 1/16th of the time. If the move says it has a higher critical hit ratio, then it will double that to 1/8th. If you use Dire Hit or Focus Energy, it will also double the probability. If you hold a critical hit item like Scope Lens or Critical Claw, it doubles the probability.
The maximum probability for hitting criticals is 50%. Exceptions: Storm Throw, Icy Breath.
The problem is that while 80 BP that ignores defense mods is pretty great, it kinda gets out-competed later on when you have 90+ BP moves, especially STAB moves. This often means the difference between killing your threat and having it come back and OHKO you, especially when levels are equal. Plus, 90+ real BP moves get their (at least) 1/16th chance to become 180+ BP moves.
That said, those 100% crit moves are useful against stall teams that like to switch in a very bulky sweep (like say, Snorlax), and curse/calm mind itself up, then sweep you. Also it makes Amnesia users look silly.