We actually spend fees on several players every season. This notion is a complete myth.
Since Sadler has taken over we have spent fees on-
2020: Jerry Yates, Bez Lubala, Daniel Gretarsson, CJ Hamilton
2021: Sonny Carey, Jordan Gabriel, Owen Dale, Jake Beesley, Olliver Casey, Doug Tharme
2022: Dom Thompson, Andy Lyons, Callum Wright
2023: Oliver Norburn, ????, ????
I'll be the first person to say that not all those transfer have panned out or were money well spent, but it's clear to see that Sadler does indeed spend money, and that's not including the increased wage budget that the club has now to bring in quality free agents or even the budget that the academy now has to sign youth players from other club.
Finances aren't as simple as simple as getting a transfer fee and immediately putting it into the "spend on transfer pile".