Why there isn't a night train between Madrid and Porto?

@seewulf is right but please do not use the rail planner app to plan. Especially for Spain, the app is very incomplete because the ever so passenger-”friendly” Spanish railways do not send their complete timetables to the European Timetable Centre. For Spain, use the RENFE website.

There has never ever been an overnight between exactly THESE 2 towns. There used to be-untill covid struck, indeed a triangle overniter from MADrid, LISboa and IRUN (+FR/ES border town), with a fairly easy change over to ward Porto somewhere in PT (I think Entroncamento).

Or even way before that there was an overnite MAD _Galicia (various towns, incl Vigo) where you could also connect southward to PT/Porto.

There probably still is an direct overnite BUS-check the usual sites that assemble all bustrips, just google

It makes no difference whatever the reason was for the actual situation. But connections over the iron rails with those steel monsters have always been very sparse from ES to PT-these 2 countries are quite different and have simply turned their back toward each other.

Is there a chance that another night train will return for this route? 

There is a chance, but not this year. The Portuguese really want a night train Hendaye - Lisbon but it takes time to organise it now that the Spanish don't want to co-operate anymore.