It is odd isn't it, esp in a football city like Manchester. You'd think it would be worth one of those blue/red/black plaques at least.
It was quite well known as the venue for the FA cup; my school used to use the playing fields right next to the stadium (in the 1960s) and I remember hoping that I was playing hockey on a cup final pitch!
Here's another link to a Reg Harris site, with the site owner's personal photo of the stadium. You can see the Toastrack building in the background
Naturally I would like to find and possibly use (given permission of course) images of it during it's glory days as a football ground but from that imagine I can quite clearly see how it would have looked.
I don't know it's capacity but at standing it must have held quite a considerable amount, though the stands don't look high up, maybe this was the reason for it's demise. Also not many Football League grounds (even now) have athletic's tracks circulating the pitch - though my team (Sheffield United) was origionally a cricket pitch and was used for both sports up until 1950's and was only until 1975 when the South Stand was built that it was properly constructed to house only football.
Looking further at the Fallowfield Stadium I noticed that the terracing wasn't roofed, the photo would have been in and around 1950's when most football stadia had roofs on the ground to safe guard spectators from the wind, rain etc; maybe this was a further reason for it's demise and would have cost too much to install a roof around the ground.
Another simple reason is as suggested in an early post that the uprising of both Old Trafford and Maine Road saw no reason for the Football Association to chose Fallowfield as an FA Cup venue and without serious cash flow from that saw little point in remaining it as a football venue.
Of course these are just an opinion and theory but I hope everyone can see where I am coming from...