I think that the reason is that normally for a horizontal trunnion it is not so critical the real location of the connection point.

I personally use another method for vertical trunnion, the one with one rigid (bend radius length) that double the bend plus the trunnion.

Offset method have advantages and disadvantages. It will consider the real length but will ignore the displacements. So it is up to you how detailed you want (or need) to model the trunnion.

Best regards,