Yes, enlarger lenses can be used, especially for close-up or macro work, but they’re optimized for a different job than normal camera lenses. An enlarger lens is designed to image a flat subject onto a flat surface, so it can perform well when photographing flat subjects at close range. For general photography, it may be more of a compromise.

A key difference is design priority: camera lenses are meant to image 3D scenes at varying distances, while enlarger lenses assume a planar subject. Also, out-of-focus rendering was not a major design concern for enlarger lenses, since enlargers aim for everything to be in focus across the frame.

Practically, the biggest drawback is usability. Enlarger lenses usually need an external focusing method such as bellows, extension tubes, or a helicoid adapter, and you must get the lens-to-sensor distance right.

So, why use one? Mainly because they can be inexpensive and can give satisfactory results for macro or copy-style work if adapted properly. Why not? Slower maximum apertures, manual-only operation, mounting complexity, and possible compromises outside the conditions they were designed for.