Baby Mario touched on it, but Kabutops's attack is revolting. It literally does effectively nothing in this format, where that damage will be Turn'd, Nidoqueen'd, Healing Breath'd, etc. It doesn't even do spread by itself; you have to run another line for that. You have to be able to OHKO things in this format, unless you're named Kingdra, who makes up for his low damage output by making that damage incredibly fast and allowing ridiculous consistency in the deck due to the discard.
Guess what Kabutops can't do.
That's right! Damage until Turn 3, by which time your opponent will have taken care of him.
Oh yeah, the other Trainer Locks are very effective though. Dialga's ridiculous amount of support as an SP (along with having an absolutely crippling Level X) and Spiritomb's awesome setup attack, along with searchablity and ability to be splashed, make them very popular and powerful.