No it's because they wanted quality figures, Sigma 6 was awful cheap figures with little to no articulation and also based of a really unpopular take on GI Joe that felt like a wanna be anime rip off. Black Series, Marvel Legends, etc have become the new standard that has been popular and are much sturdier and impressive figures. The old scale of figures while modernized can have articulation, also become extremely fragile and there is limits to how good of detail you can get without greatly increasing the cost of the figures.
Sigma 6 was like a Team America marionette mixed with anime take on G.I. Joe in an oddball scale.