The officially stated reasons for the British Army to paint vehicles was:
Preservation
Camouflage
Morale
It is true than in WW2 all sorts of matt paints were used. But that was only a short term expedient. During postwar rearmament of the 1950s there were terrible problems with paint systems which taxed the ingenuity of the Inspectorate of Fighting Vehicles & the Chemical Inspectorate.
There was a shortage of raw materiels to make the paint & a lack of appreciation of the way systems of paint were to function ie primer, undercoat, top coats. The expectation was to have a vehicle paintwork last 3-4 years, gloss topcoat was the best way to achieve this. But even the commercial motor industry was having problems with their paints. I touched on these difficulties on pages 3 & 4 in this:
http://www.hmvf.co.uk/pdf/PAINTINGpart1.pdf