The Saudis have never really needed a military, sinec they have always had ours, and they don't really have one now (besides ours). Their massive purchases of arms over the years have just been a way of cementing their relationship with the US, which made some sense when they were worried about Soviet-backed threats to their rule, or later Baathist and Iranian threats.
At this point, though, the only threat to their rule is from other Saudis, so there is little reason to court US protection.
When you think about it, though, what does a country with no military do with massive arms purchases? We have always said they buried it, stockpiled it, in the desert to be used by US brigades who might arrive in an emergency and be immediately supplied from Saudi stocks.
If its buried in the desert, though, who is to say it exists? Who is to say that the "arms purchases" weren't massive bribes which purchased American military protection. Or they were underwriting "off-the-books" enterprises that wouldn't show up in the official budget. It might be significant, then, if Saudi bribes were being diversified to include Moscow's ruling elite. It may simply be a way of expressing some pique, by reducing the payoffs to their former American friends.
I know, I'm crazy.
Saudi Arabia along with Egypt & Turkey have among the best equipped militaries in the region(taking Israel out of the equation).