It is hard to describe what would become clear with an illustration. True, the spring pressure is more or less linear. The Bending Moment comes from the fact that the Sear/Cocking Piece interaction is off-axis, thus establishing parallel, but off-axis forces. These parallel forces constitute a Bending Moment.

Concerning the bolt being locked by the Striker: it is locked each time the rifle is fired. You don't realize it because the Striker is cammed back by the bolt when the bolt handle is lifted. If the cam surface is missing (as when the Cocking Piece breaks off), the Striker cannot be retracted. Ergo, the bolt is locked.

Now early Mausers didn't have this feature and I suppose this may be true of some Siamese rifles.

Hope this helps.