He has been backed... but by the club.
You seem to forget that the scope to reinvest sales into the budget would've been far greater back then due to much lower overheads, a less of a demand to pay decent fees for players and player turnover of course being much higher due to many being on shorter term contracts.
The first summer of L1 the club had received dividends from the PO run and promotion, a windfall from Maddison's sell-on clause, as well as McNulty being sold to Reading. That was a sizeable amount of revenue raised comparative to our turnover at the time, you'd think at over 50% at a guess, so you can see why there was scope to pay fees for players such as Bakayoko, JCH and Hiwula. Unsurprisingly that year SISU extracted significant funds totalling £1.6m from the club as well.
The following year Chaplin and Bayliss were sold, which also allowed Robins the means to purchase Godden.
The difference is now though we haven't received a windfall for a transfer since Wilson was sold two years ago and the last player sale was McCallum in January 2020.
The pattern is quite clear, without revenue generated from transfers the budget available for purchasing players just isn't there. Certainly not when this season wages are now 100% of turnover, transfer instalments are due for certainly one of Sheaf and Gyokeres but probably both, improvements have had to be made on the Ryton pitches, the club are stuck with players on significant contracts that seemingly can't be moved on, SISU could potentially extract funds to repay interest as they haven't done so in three years, and there's a £2.4m loan to the EFL in need of repayment by 2024.