If League Two was significantly stronger than the Lowland League then you'd expect the clubs to bounce back immediately but not one team has gone down and won the Lowland League and, this season, the teams aren't even close.
Being relegated out of the SPFL immediately makes a club less attractive to players. This is for a club that has been on the slide (East Stirling a possible exception to that, since they perennially tended to struggle) and so less likely even to keep the players they had - who weren't good enough in any case.
Being promoted tends to mean higher crowds and a higher budget.
Hence being relegated means a lower budget and lower crowds.
Is it any wonder no team has yet gone back up?
It would be a miracle of sorts if one ever does bounce back straight away.