I think the problem is not that it can be opened from the inside but more that the ones that just have a lever to flick on the inside are usually yale style locks that are easy to bump or pick, or break a window and reach, or put something through the letter box to reach.
The mortice locks are harder to pick and are usually substantially sturdier in construction. In the UK at least, the mortice lock is physically inside the door structure (1) whereas the latches that don't need keys are attached on the door (2).
We recently had a break-in in the block of apartments where I live where the latch attached on the door was broken off by people forcing a door. If there had been a mortice lock, they'd have to break the door frame or the door itself, rather than just bust the weak latch lock off the back of the door (in this case the door opened outwards, so they just pulled on the door handle whilst bracing a leg against thethe wall and the latch came right off the back of the door)
1 - https://www.buildingsheriff.com/mortice-lock-costs_files/sta...
2 - https://www.diydoctor.org.uk/images/nightlatch.jpg
