Why do these pits keep appearing behind me?

It's a puzzle, that's why.

Did you see anything near the entrance to this area?

Like the lever?

And the two written messages?

The pits can be closed by pulling the lever near the entrance.

Unfortunately, you can't get to the lever once you've entered the area.

So you need to find another way out.

If you're careful, you can get through this entire area, pick up almost all
the items, and still reach the exit.

I said almost all.

If you get the boots, you'll have to jump down the pits.

This isn't necessarily bad, though.  You can get back up.

Did you see anything else near the entrance to this area?

Like a set of stairs?

If you do fall down the pits, you'll end up in the southern portion of level
6.  The stairs back up are to the west.  It's actually a good idea to fall
down some of the pits, as this area is locked from the inside.  Once you've
gotten all the items in this area, you can go back up to level 5 and try the
pit puzzle again.

Are you still stuck?

It helps if you go west at the first intersection.

After going through this hallway, you'll be in the southern part of the pit
area.  Head north when your way is not blocked by pits.