Ti is tougher than steel, it will not harden into the ranges steel conterparts can. There are two qualities to rifle actions, 1. Hard and 2. Tough. You need a combination of the two, this is why 4140-4340 is common in the chrom moly actions, it can be hardened to withstand the pressures but also made tough enough as not to have the abutments beaten. It needs to be resilent, able to flex or spring back. Titanium has these same qualities, if you ever had to machine or drill and tap some you would understand, it will turn a drill bit red in a second if not carful.
Machining hardened 4140 is very simple, chips come of easy and smooth. Ti dont like to let go of its chips, when drilling the hole it will want to close in on its self, the same with tapping. Special tools are required with messing with Ti. Actions are more expensive, Ti ain't cheap and machining the parts is about 3 times longer. Of course a pound of Ti is way stronger than a pound of steel, Ti is 55% lighter than steel. If Ti wasnt strong as steel, they could not build factory rifles out of it safely.