Heat dissipation. The engineers expect the lamp will not be able to handle the power -- to be more specific, the lamps have not been tested at the higher power. And so the UL listing and the instructions do not permit this. It is illegal to install or use an electrical device contrary to its listing, labeling or instructions. (not least, your homeowner insurance could refuse to pay).
Power is relevant because all available bulbs convert almost all of their energy into heat, so a 13 watt bulb makes 13 watts of heat (well 11 or so with the most efficient LEDs, but close enough).
Given that the LED revolution is here to stay, and IKEA has bet the farm on it, there is no earthly reason for IKEA to drive up the cost of their luminaires for everyone merely to provide significant thermal protection for the 0.1% of diehards who insist on using obsolete incandescent bulbs.
If supporting the heat output of incandescent or large CFL bulb is a requirement for you, don't shop at IKEA and shop at a lighting specialist store who understands the requirement. Keep in mind with CFLs there are also bulb-orientation issues, they really should be socket down for cooling. Honestly today, LEDs are so good that there's no reason to use CFL, except blacklight (fluorescent being a good source of ultraviolet).
Beware the lumen chase
Now that "lumens" are the new "watts", it's very easy to get wrapped up in "Lumens per watt" or "lumens per dollar" and chase numbers. That's a mistake; that's how the government came to believe the economy is doing great when it's not.
The classic problem of every light up until LEDs is that they all emit light in all directions; that's great if you want to light the inside of a sphere. And we have been stuck with "sphere-lighting" bulbs for 110 years, and that is woven into our thinking about how lighting is supposed to work.
Lumen testing apparatus, measuring how well the lamp lights up the inside of a sphere.
Actually, what we want in almost every case, is to light up a "cone" or "wedge". And so we have "made do" with reflectors that aren't very efficient (or the awful "paint the interior of the fixture white" tactic.) These are better than painting it black, sure - but not very efficient at all. So from a spherical bulb, much of those lumens are absolutely wasted.
(from this great source)
Lumens are just a stop on the road to lux.
Along comes LED. It inherently lights up a 120-140 degree cone. If you know some trig, that's about 1/6 of a sphere. How does this work for lumen measurement? Lumens are measured in a sphere - so an LED only gets credit for about the 1/6 of the sphere it lights up. That means for same-lumen bulbs, an LED is much brighter in-cone, and much dimmer or black off-cone, of course.
Now back to the part where we actually do want a cone. Obviously LEDs are a gigantic "win" in this department. Their 140 degree cone also lends itself to using lenses instead of reflectors, which are vastly more efficient.
Unfortunately humans are so inculcated into the concept of spherical light and that stupid dome. So most screw-in LED "bulbs" are intentionally made to light the inside of a sphere. They are made as universal swap-in replacements, and they just light every direction so nobody has to think about aiming.
LED is a much better deal on bulb shapes intended to be conical -- such as the PAR "reflector" bulbs.
Another example is fluorescent tube fixtures: they waste most of their 3000 lumens on inefficient bounce light, and LED "replacement tubes" use this to great advantage, giving brighter light with 1600-1800 lm by aiming it properly.
Light-on-subject is the only light that matters
So, since you're mentioning that you're a photographer, what you really want is light-on-subject. That isn't lumens, that's lux.
I can't tell you how many 175-watt (225W actual) metal halide lights I've replaced with a $9 cheapie 10- or 15-watt LED flood light, and ended up with more light (lux) where it matters. Mind you, metal-halide lights are already the same lumens/watt as LEDs, LEDs are more efficient only because of aiming. In another project I'm replacing a blistering 3150 watts of metal-halide lights with 150 watts of well-aimed off-road spotlights. I mail-order all that stuff (and it's not subsidized). I'd be reluctant to use it for photography because the China-via-Amazon vendors don't super care about color temp or CRI.
$10 cheapie flood light (140-160°) and $20 12V spot light (30°, also available in 60° and 8°)
Honestly for high CRI, my go-to is actually 48" tube fluorescents. Tubes and fixture for $16 and you have 5000 lumens right there (poorly aimed of course). It's sorta like the way steam locomotives and carburetors got really good right before they went obsolete.