I have a 403(b) from eons ago, small amount ($2000.)

I was told I could roll it over into my current 401(k)

Is there a reason I shouldn't do that?

A coworker said there were some tax advantages to 403(b) but could not elaborate.

Roll it into an IRA.  there are advantages with regards to inheritance tax if something would happen to both you and your wife.  IOW, if you would die, your wife could inherit with out tax in any situation, however if it goes to children they would pay tax on it.
It also puts all the money in a fund that only you can get at.  I see no advantage in rolling into a 403b.
I am surprised they didn't force you to roll it over already.  Most companies have a 5K cuttoff for rolling over or taking funds.