There are actually significant benefits and opportunities available to TFA corps members following their two years in the program - if you look on their website under benefits and opportunities there is a huge list.
I think the idea is that future leaders who commit to teaching for two years in an urban school should be recognized and rewarded by companies and other schools in the form of employment deferrals or waivers for application fees. TFA works to create this network because they want to produce a corps of future leaders, regardless of whether they stay in teaching after their two years are up (I think the idea is that they will retain their passion for closing the achievement gap and battling educational inequity by donating to TFA and supporting future TFA corps members). Schools recognize that TFA is an elite organization that selects their corps members with an eye on that leadership potential - there is a lot of overlap.
Coming from a family of educators, yes, it is somewhat frustrating that regular teachers cannot take advantage of these opportunities, but in many cases, they will be staying in their schools or in the field of education for longer than two years and so wouldn't necessarily find an application fee waiver for business school to be that attractive.