If time travel is possible, and has occurred, then there is a good chance that the creators messed up the space-time continuum, and traveled back in time to destroy all traces of time travel so it can never be created in the future.
If your scenario admits that time travel is a possible invention then it would have to admit that more than one human could invent it. Thus even if it's initial creator went back in time and destroyed all remnants of time travel it does not preclude the possibility of other humans discovering it and using it for a different purpose. Also, the initial inventor could not possibly fix all issues with the space time continuum even if others could not invent time travel behind them. If they went back in time and destroyed all remnants of time travel's existence they would either have to permanently remain in the time period they made the change in (thus altering the space time continuum) or kill themselves in that period of history (thus altering the space time continuum)