One of the sad conditions accompanying a success in America is that demand always outstrips supply, often for long periods. We see it in electronics, automobiles, and even clothing. With the upsurge in purchasing of firearms that started when Obammy took office, and has continued unabated as both laws changed to enable CCW, and with the simple-minded posturing of Obammy, his appointees, and various Altzheimer-like Congressional Representatives.
Manufacturers usually manufacture magazines based on a percentage of projected gun sales. Not everyone wants, or NEEDS, a half-dozen magazines for their gun. Funnily, many are shipped with TWO magazines from the factory, and lose one to Distributors, or Dealers upon arrival. Sig suffered the same fate in the early 2000s. It's NOT Taurus responsibility to police what anyone does with it's products after they are sold. I bought a PT709 Slim last year. It came with 2 magazines. I purchased a PT638 on Black Friday, and it also came with 2 15 round mags.
Unlike small businesses, larger manufacturers, especially in today's "just in time" business model , have to plan runs making models, parts, and spares like magazines. Being human, they aren't always capable of reading the American market. Add to that the fact that America is one of only a few nations where "military calibers" are allowed into the civilian population.
Like with rim-fire ammunition, WE are the reason that supplies are running out on a regular basis.