As one example, C++ has had non-type template parameters (types parameterized by values) for a long time, but only for compile-time constants. AFAIK there have been no formal proposals to introduce full-blown dependent types, rather the focus has been on improving the facilities for compile-time term-level computation.
Knowing that a list has length n at compile time isn't that useful if you're expecting the program to change the list's length at runtime. Or maybe there was never a list in the first place because it was null.
The type systems in mainstream languages were not built with these kind of flexibility required by dependent types.