Banknotes and Footballers’ Portfolios

I spoke with a well-known banknote dealer/seller a few days ago. I was told a number of Premier League footballers are collecting banknotes to ‘increase their portfolio’. Banknotes are seen as a good investment. For sure, the footballers have financial clout but ‘portfolio’???? I think bank note sellers  and collectors hardly use ‘portfolio’ in thinking about notes. We try to build up the collections as we love the hobby. Perhaps the footballers will push up the prices but I imagine they would be after the high end only and ignore the middle of the road notes. I hope they find another interest such as stamps, bowls, gold coins, tapestry, or even taxidermy!