I agree that wrapping is a bad default, but I can provide some rationale.
If you do wrapped addition without flags, you have one self-contained instruction that even covers signed and unsigned integers. If you want other behaviour, you then have to specialize for signed or unsigned, specialize for the choice of wrap/trap/flag, and make those traps and flags work nicely with whatever other traps or flags you might have.
So, yeah, if you want the simplest possible thing, driven by some decision other than the best outcomes for software in general, then you would choose wrapping addition without flags or traps.
If you do wrapped addition without flags, you have one self-contained instruction that even covers signed and unsigned integers. If you want other behaviour, you then have to specialize for signed or unsigned, specialize for the choice of wrap/trap/flag, and make those traps and flags work nicely with whatever other traps or flags you might have.
So, yeah, if you want the simplest possible thing, driven by some decision other than the best outcomes for software in general, then you would choose wrapping addition without flags or traps.