The dozer is an optional vehicle that helps speed up the mission.
Not everyone uses the dozer (as it is specialised to only some areas). The only way to make missions requiring the dozer, would be to put the dozer under an expansion wall or else it would impact all the players who don't use the dozer.
I normally dont disagree with you, but on this i shall - considering the dozer has been around for over a year, thats a pretty lame excuse, also if it was just to speed up - it should be along the lines of 1 every 20 (15 with premium) wildland expansions like the other speed up units, also if it was just introduced then id kinda agree- because thats what happened to the MCC. And along the subject of required units - the original developer had certain units required at specific station levels - maybe new units added could be done that way.