As a weirdo who bought a GT but had them swap the 17's for it I can fabricate a reason why this came about:
the specific 19" tire size has a single tire made by Kumho and (Toyo?). Go to TireRack, Tires.com, etc. and search the 19's size and become dismayed by the lack of choice and outrageous price (same exact Kumho on the 17's cost 50%). I LOVED the look of those 19s, but come on Mazda, the CX-5 ain't worth $900/tire change.
More likely, your dealership is stalling for time. Salesmen don't know squat about their own product, let alone the logistics of what's coming to port. My wife's CX-5 test driver explained how the CX-5 had rear seat ventilation ports in the back of the center console. IDK, maybe the nitwit thought she was blind? Subsequent sales mgr. (trying to force an on the spot sale) explained to me how awesome Mazdas were in comparison to much smaller companies like Subaru - who only make like 3 vehicles. ??? Point is, they will say anything.
No harm in talking to another dealership to see what their line is on the situation... most dealers have NO loyalty to you, don't fool yourself into being loyal to them.
BTW, we picked ours up on the 25th from the best-rated dealer in Georgia... they had to drive it in from N.C. because they're selling so hot. ...with as hard as they looked, I would've heard the same line, I imagine, if true.