It is also easier for them to maintain wooden coaster as the cost of custom making wood pieces is cheaper then fabricating and installing steel track. Plus no matter how much you "protect" steel, it will rust and degrade over time. That is why you still see some old woodies around.
**I am editing this post for those who need more explanation***
It is cheaper to repair small sections at a time as in a wooden coaster than it is to replace steel sections of a steel coaster.
The wooden coaster requires wood that can be cut to size and replaced by the park maintenance staff with normal carpentry tools. A steel coaster, if a section of track or support goes bad that whole section has to be replaced, which would mean that the process of building a new piece of track and replacing it is far more costly than a wood coaster. For one, the part would have to be fabricated by an outside company which will cost $$$$ since track is not available due to Arrow no longer being in business. Yes, I know normal maintenance parts are available from S&S. Plus I will bet you S&S will not want to keep making parts, because this will require to have tooling setup to make these few parts for these old coasters. After so long; when the demand goes down, the cost of keeping the old tooling creates a monetary loss for the company. So since steel sections last longer than wood, by the time the track needs to be replaced, it would be an exorbitant amount of money to repair a 25 year old coaster.