If you were the new owners of Newcastle - inheritors of a dysfunctional club, but with a massive budget even by EPL standards to turn things around - why would Gerrard be viewed as a top candidate to entrust with the rebuilding project? Granted he has done well at Rangers, but does he have the requisite depth of experience to take over a team who play in the most competitive league in the world and fulfill the ambitions of the new ownership? I'd say no.
If you take for example Brendan Rodgers, who had managed to build Swansea into an overachieving team, then brought Liverpool to within a hair's breadth of winning the EPL, coupled with his experience as manager of the bheasts, this is the sort of CV that if you were an owner of Newcastle that you'd feel comfortable entrusting your investment to. But Gerrard has nothing like this range of managerial experience to offer. In terms of his managerial pedigree, he still has much to prove.
Like his great midfield rival Frank Lampard discovered, managing a team with huge expectations, with a wealthy, ambitious owner constantly breathing down your neck, isn't that easy. The situation he took on at Chelsea was a one that required an experienced manager - which Lampard wasn't. The difference that we saw at Chelsea when an experienced manager (Tuchel) took over was dramatic. Tuchel, within a season, managed to transform largely the same group of players, into Champions League winners. As I said at the outset, Gerrard still has much to learn as a manager. IMO, he'd be well advised to resist the Newcastle siren song and remain at Ibrox for a while longer.