For some reason, while level 10 characters still have PK protection, they are no longer able to use recall.

Without recall, low-level exploration of SK is simply too hazardous. Even in areas built to include level 10 characters, there's often some high-level monster that's hard to flee from successfully. On the other hand, recall works unless one is completely overwhelmed by lag and/or damage.

It would be nice to either extend recall to level 10, or end PK protection at 10, so it's clear what level the inexperienced should stop at, if they want to continue feeling their way around.

I'd much rather a newbie get lost or stranded without recall the first time when he is still safe from PK, rather than lost or stranded without recall the first time when he is a sitting duck for killers.

True newbies don't tend to level that quickly, and have a good chance of getting the "you can't recall anymore" message loud and clear while they are still level 10. It'd be pretty painful to get that message the first time at level 11 when you see a group of nasty PC adversaries enter your vicinity and you try to 'recall' to get away from them!

I am unsure if one level will change that much when
aggro npc/mobs will attack you at level 9, compared to level 10.
To be

I think the loss of recall at level 10 is a great motivation
and incentive for newer players to stop rely on it
one level away from the PK rank.

The only difference between level 9 and 10 in exploring
"safe" areas is 10-20 movement points and health (give or take).
That really is not going to change a lot.