Cherries + yellows is a no-no. Here's the chart of
Shrimp Types Which Should/Should Not Be Kept Together. (Amanos are safe with either but require different water conditions. They will live but will probably not breed anyway in a tank set up for cherries.)
As to why not let them hybridize? For starters, it's a bad thing for you: the offspring will be worthless as far as being able to sell or even give them away. Even if they look like "true" cherries or "true" yellows nobody will know if they will breed true since they might have the genes for the other type mixed in. Therefore they will most likely not be willing to take your stock even for free.
It's your choice of course. You might get lucky and produce a red/yellow striped variant that will itself breed true and they will be wildly popular and you will become rich.
Much more likely you will get offspring that are just muddled messes with no particular color at all. The two types have been carefully and selectively bred only to ones of the same color for many generations to get them to where they are today. If that gets messed up the tendency is for all the selective breeding to go out the window and offspring revert to looking like the "wild" type.
that's my understanding anyway. I'm sure we have some genetics experts here who can explain the matter in greater detail and accuracy. Why not do tigers instead of yellows? They're in the "safe" category on the chart and (imho) more attractive anyway.