Masterly Steel weapons have a brutally high DC and crafting-point requirement for the specific niche they serve. Novice crafters won't be able to make them before they can find better weaponry, and expert crafters don't want to waste crafting points making them. This leads to them being out of the price-range of anyone who would want to use them. By the time most characters can afford them or make them, they have better options available to them.
The prevalence of stopgaps like Flame Weapon and Greater Magic Weapon scrolls further exacerbates this, as you can potentially grind past the need for a masterly steel weapon entirely, grab a greensteel weapon -- which are less crafting points and a lower DC to make, and arguably just as good or better -- and coast until you can get your mdamask or +4 weapon.
As I am to understand it, the high-cost was warranted because these weapons could otherwise be easily mass-produced and tossed into a basin for 5% rolls to keen. However, now that hard 5%s are nixed, it makes sense to for the high cost of masterly steel weapons to be reevaluated and adjusted down accordingly.