Looking at the pins available on a 25xx-series part, I'm reminded that there's no BUSY output, nor indeed any way of checking the device status without an SPI bus operation.
There's a HOLD input, which can be used to... uh... put the chip on hold while you use your SPI port to talk to some other SPI peripheral in the middle of a bus operation. Which I'm sure is totally useful. To somebody, somewhere in the Multiverse.
But, a BUSY signal, that could be used to, oh, provide an operation-complete interrupt on a multitasking system? Nah.
Because, really, whose CPU has anything more exciting to do than busy-wait on a status bit reached through SPI bus transactions?