I have no idea why (probably cruiser salesmen or something), but the preposterous idea that you MUST be able to flat-foot a bike with both feet has really taken hold.
Perhaps that's true for beginners, or perhaps in places where earthquakes at stoplights are common. But if you have the skills, you can ride whatever you want.
My personal favorite illustration of this was a 5'4" friend of mine who was curious about my KLR650 and borrowed it for a ride across town. Not only is it a very tall bike in the first place, but the suspension is set up to suit me, and I weigh about double what he does. The suspension barely moved when he clambered aboard.
He's a skilled rider, so no problems at all. Granted, he had to slide sideways off the seat at every stop sign and leave one thigh draped over the seat...
Another friend who's a fairly skinny 5'6" has ridden my Vee a few times with no troubles. It's wearing 5/8" raising links, plus the suspension is set up for a much heavier rider -- about as tall as you can get. Again, no trouble at all even in city riding.
2002 Suzuki DL1000 V-Strom, Dark Metallic Space Blue
1983 Suzuki GS850G, Cosmic Blue
2005 KLR685, Aztec Red - Turd II.2, the ReReTurdening