Over time, cryostat manufacturers began favoring disposable blades because they section more cleanly than permanent blades. Nowadays, the majority of cryostats accommodate disposable blades exclusively.
Of course, that's not to say that permanent blades have no place. For labs on a tight budget, buying a few permanent blades and sharpening them regularly will be cheaper in the long run than constantly resupplying disposable blades. Additionally, permanent blades are ideal for remote clinics that may not have constant access to disposable blades.