Because they decided not to support the older technology w/ Windows 7???
Heck, I don't even see Windows 7 32-bit in the driver package:http://188.8.131.52/airlive_fileserver/uploads/English/support/SD1228117968123.rar
But it's always possible the drivers are available from MS and will automatically install when you insert the USB adapter. Have you even tried?
If it's not available from either the manufacturer or MS, you're stuck (I suppose you could try Vista64 drivers, but I can't guarantee it will work).
Sometimes manufacturers just stop support once the item is considered obsolete.