Costs, and necessity.
It costs money to 'change over'. But, the fact that a large number of the layouts I visit run 'other than track power', it has been necessary to have some 'away' stock. Nothing flash, just a battery, and on/off switch.
Having since experienced (the cost of) my first battery failure (it wouldn't recharge..... kaput), I am still convinced of the benefits of Track Power.
One of the claimed 'faults' with track power, is the need for clean track. So they say. Very rare for me to clean track, as I use the rail oiling method. What a lot of anti track power advocates fail to see, is that it is not always dirty track that causes stalling etc., but, rather 'poor' track maintenance. Twist in track, especially near dead frogs is a common complaint. Twist causes one, or more, wheel/s to lose contact with the rail.Just pack the track right, and away you go. Stalling on points... more often than not (apart from the above mentioned twist), is the plate below the switch rail, make sure it is clean, and making good contact.