The best LEDs are now remarkably close to the theoretical maximum luminous efficacy. We're now bottlenecked by batteries and the limits of sanity.
Specialist diving companies will happily sell you a 60w, 6300 lumen flashlight. It's not a big market, but it exists. To run a light like that you need a massive external battery pack tethered with an umbilical, because it'll eat through the entire capacity of an 18650 cell in under 10 minutes. That's no problem for divers, because a properly designed battery pack is close to neutrally buoyant; it's a major inconvenience for people on the surface.
1000 lumens is Good Enough for 99% of users of handheld flashlights. There really aren't that many people who need to throw a beam for half a kilometre or light up a football stadium with a flashlight.