There's any number of reasons why an a/c might RTO. They might include equipment failure, or crew incapacitation, or workload, such that they can't report stopping. The ATCO should be watching the SMR (if available)...or the radar (if available) or failing that, an airborne report, to ensure the runway is clear for the next one. Any other way is simply not fail-safe.
A "stopping" call is good but I'd only expect MAYDAY or PAN if you required emergency assistance.
(I'm based in the UK fwiw, I know the US have different rules on runway protection and clearances...)