why is it that a larger number of LW users cannot be browsed?

They're getting smarter and realizing they can choose to turn it off.

You don't let me browse, I don't let you download......door swings both ways! Give me a better reason, and I'll stop the practice. 'Til then...

Some people live in hostile areas where allowing a browse is literally suicide.
Even in Canada or Finland it is a very bad idea if you have any copyrighted files.
That good enough for starters?

Just because you can't browse doesn't mean they aren't contributing, and in
fact they are probably sharing more than you are, which is why browse is off.

Stop thinking of gnutella as a trading network and allow others some freedom of choice.
The door does swing both ways, so let it.