Anne, since the bladder lining has been "transformed" and is unstable with regard to tumor formation, and has demonstrated this either by spreading into the muscle layers or by repeated returns, chemo (which might attack current tumors) would not be effective in halting the cancer in the bladder itself.
The purpose of chemo prior to bladder removal is to destroy any micro-seeding of metastises outside the bladder. Since bladder removal is major surgery, and requires a relatively long recovery time, chemo given before bladder removal is more efficient than waiting six months or more.
Occasionally, once the bladder is removed and analyzed, it is found that there is more likely to be a spread of the cancer than was originally thought, and chemo is done after the trauma from the cystectomy has healed.
Sara Anne