Just curious — Crown xls 5202 amplifier

I was watching a YouTube video on the Crown xls 2502 amplifier.  It is rated at 400 wpc at 8 ohms and only costs about $650.  I was curious as to what guts this thing has underneath, to create that kind of power in a slender cabinet.  But when the reviewer took the cover off, I was surprised at how little there was inside this thing.  There were 4 (what looked to be) filter capacitors, a small transformer, a small coil that looked to be copper and a couple of smallish heat sinks.  It didn’t look like anything that would produce that much power.

Do you know how this technology works?  If it is able to produce so much power in a small space, why don’t more manufacturers build their amps this way?

(The reviewer noted that such amps are used in commercial applications and this amp was noisier and did not produce as full a sound as some other high-end amps.  Still, I would think a lot of guys would want that kind of power for such a low price).
It is a Class D type of amp.  
I've owned clubs, Crown, QSC, Crest and others have huge power ratings.  They really crank but with limited bandwidth and 1% distortion levels.
Put one in a home system against a 400 watt McIntosh or similar and let your ears do the rest...
I read that the amp is Class D, but I don’t know how they get such power generated from such sparse innards (when compared to my Parasound A21, for example, which is rated at 250 watts RMS into 8 ohms).
Basically chip amps...
And they don't do complex subwoofer loads especially well.
Still, I would think a lot of guys would want that kind of power for such a low price).
And that one myth has probably been the downfall of many systems. In the "golden days" (whenever that was 60'-70's )high powered amps were not readily available.  Oh sure. professional studios and venues had them . But the typical  PA' system only had 200wpc or less. I've sang over many of them. High wattage then was 60-80wpc. The key is that it was known that high watts doesn't necessarily have good sound. Today, I see people constantly talking about the "Need" for a high powered amp 300-400 wpc as though it automatically meant that it was going to sound better. FWIW, I have a 1200 wpc Crown in my PA. I've had 1200 wpc to 35 wpc (Which I have now) The 2 best sounding amps were 35wpc tube and a 45wpc Harmon Kardon. OK, I'll slide my soapbox under the table now and get out my flame retardant suit.

Technology marches forward! Still, I'm holding onto my Perreaux 2150B - 340/680/920 wpc at 8/4/2 ohms! And the size and weight of a good anchor!
I have a crown xls 1500 I got used for like $200. Lots of power and on it's own sounds a little sterile. Mated with tube dac and pre it actually sounds very nice indeed. Several of my friends were very surprised how good it sounds. 
I do live sound mixing/producing for filthy lucre, and although I have pro amps around I would never use them for my hifi...the high power of pro stuff gives you the headroom needed for uncompressed sound and live systems rarely use all of it...powered speakers are generally cruising along as they're generally very efficient, as are pretty much every type of live speaker I've used. I had a pair of Altec A7s for my bands in the 70s, driven mostly by a Kustom "Bi Amp" that had 200 watts for the woofers and a hundred for the horns...loud. Note that in a Magico factory tour I noticed a QSC GX3 amp like the one I have on their shelf (an inexpensive masterpiece of a powerhouse amp, what does Magico use it for? Hmmm)...I occasionally use mine for monitors or whatever on some live shows, and in its little road case it's generally used as a footstool for my wife's home office chair. The fan noise makes it unusable in my studio so I use an old Alesis RA-100 in there. My hifi amp is a massive 12wpc single ended tube amp, and I won't be using that for live stuff.

Have never heard a Crown amp that in a 2 channel system didnt sound terrible.