This a worthwhile discussion to have. I'd also be of the "last minute" variety and especially with circumstances these days, I find it very difficult to know if I can attend something until the day before (and sometimes not until the day itself). Having said that, printing maps is time-consuming and costly so an early cut-off is understandable. I wouldn't have a major issue with a small amount of waste, especially as the ability to pre-enter gives a good indication of likely numbers.
A compromise solution might be to incentivise pre-entry with reduced rates. Those wanting the flexibility of entering on the day should be happy to pay a premium to subsidise the risk of printing unused maps. This premium could vary depending on the weather forecast 🙂 It'd be interesting to see the data but I'd imagine there's a fairly even distribution between those who pre-enter and those who prefer entry on the day.
As for pre-entrants expecting maps (which I fully agree with), the solution to that could be to have a reasonable cut-off (say 12pm) with EOD only allowed to start after that. If there is a map shortage, especially for pre-entrants arriving later, a finisher could be asked to lend their map and have a fresh copy given to them at the next event.