Stop illustrator from disabling file recovery

[Prion]

I enabled file recovery earlier today. did not tick 'disable for large files' 

Took it upon itself to disable file recovery automatically

How do I prevent this from happening in the future?

[Monika Gause]

Did it crash?

"File recovery" IS NOT a proper backup strategy. Your files might still get corrupted in crashes or the recovery might save during a power outage and the recovery archive is then unusable. ALWAYS make proper backups.

I get it that when you're "in the zone" or under strain backups are not the first thing that come to mind. So if you cannot remember to backup regularly, get the plugin Autosaviour (a free version is available). It will save one backup for you regularly. Since it saves a real AI file, it might interrupt your workflow slightly. But this should be worth it to have a proper backup.