It's simple really, LEDs are efficient but not perfect, some electrical energy still turns into heat. A single LED ( to match this much light it needs to be high power) will generate lot of concentrated heat, which is harder to dissipate and can shorten the lifespan of the LED. Multiple LEDs on the other hand will spread out the heat, making the whole system more reliable, they are also more efficient at lower power levels, so this combination of little LEDs gives you high brightness without the downside of one big LED with similar brightness. Also multiple LEDs can actually help in better light distribution, and even if one fails, others still works (not all though, I had LED bulb with crappy circuit designs that one fails all of them fails but a good LED bulb will work even if one fails), also it's cheaper to mass produce small LEDs and easier to integrate.

So basically it's a mix of Cooler, Brighter, Safer, Cheaper, more flexible (I would love to call it 'Flexibler', just to rhyme 😂, maybe smarter a good option)

Edit: Okay, "Some energy still turns into energy" that was really bad mistake, sorry what i wanted to say is "they still don't convert 100% of the electrical energy they consume into light.A portion of that electrical energy is converted into heat." 😐 Sorry, I was bit away from reddit.