I am not 100% sure about that. Southgate went for consistency/loyalty when in fact we probably had a historic level of talent.
It might have backfired for the lad, Nigeria having issues paying players even before the recent currency collapse.
Not an England fan myself but they do appear to have an abundance of good players at the moment. For some of the dual qualified players they would probably struggle to get a handful of caps whereas they may reach a fair number with other countries.
Matty Cash, Michael Olise spring to mind.
Carl Jenkinson also springs to mind, switched his allegiance from Finland to England and got one cap in a friendly, probably could have amassed a fair few if he stayed with Finland.
I know the English FA have been courting two of our youngsters recently (Charlie Crew, Leeds & Lewis Koumas, Liverpool) It does appear to be trying to take them for the sake of it when you look at England's player pool compared to ours.
On the England front the young boy at Port Vale (Dipepa?) looks one for the future.
Many years ago the English FA approached Gareth Bale (his dad is English) but thankfully Gareth knew where his roots were.