Remember Lenny's experience when he left Celtic to join struggling Championship side Bolton Wanderers. Although admittedly Bolton had far too many troubles already both financial and playing wise and turning that around would have been some achievement, Lenny was completely swamped and absolutely out of his comfort zone, he couldn't cope.
The lesson though is it takes a club in dire straits, and in that case a struggling second tier one, who can't attract a quality manager to look to Scotland. The days of Sir Alex and Aberdeen's manager being recruited by a first tier club have long gone.
A reminder that when United approached Fergie they weren't perennial winners but had been in the doldrums for years, had been relegated in recent memory, and only ever seriously competed for domestic cups being well below the top standard.
Fwiw the reputation of Scottish football isn't that great in England, Brendan Rogers move south to Leicester very much the exception and not so much of a risk because he'd already been proven his worth in England before Celtic. Lennon would have been a huge risk for any prem club and Gerrard has no proven record in the prem to attract real interest.
Managing Rangers or Celtic you should always be top two and it doesn't take a top drawer manager to win titles. It's understand then how mid table clubs in England, who with the TV riches can now pay very well indeed, might be firstly drawn to managers of a higher calibre or if they're not realistically attainable then at least those with a proven record in England, Stevie G. has neither the pedigree or proven record in England.