As others have said , plenty of TOC's & FOC's will have been caught out in the past . Relocating whilst also completing your training be it at school or practical handling is likely to have an impact on your progress . And there is always the risk that even if you have the best will in the world you could have property sale/purchase fall through meaning you are not relocated within time .
I know plenty of other jobs will allow relocation , but I don't know of many safety critical ones that would , on the railway I know the same applies for signallers for example . Ive seen vacancies for pilot training schemes that give geographic restrictions . And once in post as a pilot or cabin crew there are requirements that apply to be able to be on location within a set time when on standby so if you do not relocate it is likely to quickly have implications for your continuing employment .
Take Air Traffic Control if not, Apply for N.A.T.S, they don't care where you come from as long as you are in position for day 1 of the role
Anyone applying for NATS though would be aware that they will be trained in either area or approach control , and once trained can be posted anywhere accross the country depending on the needs of the business . Slightly different from applying for a given vacancy at a set location . The whole premise with NATS is that it is more likely than not that you will be relocating once trained .