It has to do with the diodes that are available. Pointers aren't a market for diodes themselves, so the diodes get taking from other products like DVD burners, BluRay burners, projectors, etc. 300mW is about the strongest a RED diode needs to be capable of producing in order burn DVDs at that fastest speed DVD disks can safely be spun. So there isn't a big market for stronger RED diodes.
Having said that, strong red diodes exist, but instead of bajillions being made each year for common optical drives, you're talking about fractions of that many being made at higher powers. So you *could* find a stronger red diode if you wanted, it would just be very expensive. However, you probably could push one of the diodes you've seen running at 250mW up to 350mW. It might have a shorter life, and get hot so quickly that it's duty cycle would be low - but it's doable.
I have a 635nm diode capable of as much as ~380mW, but in addition to costing ~$200, it is also incredibly complicated to actually focus into a beam (beyond my abilities)
better than people sounding like there talking to the air...
