It's the same reason Nintendo didn't license DVD playback for Wii even though the hardware is perfectly capable of handling them. Money.
The problem I see with Switch is that as of right now, it looks like a psp/vita in that on paper, it looks more like a portable you can plug into a TV. However, it's being marketed as a home console you can use if your parents want to use the telly. This means that a lot of people are expecting home console (ps4/xb3)-level specs but they're worse and it's more expensive than a ps4 or xb3, to boot! Trying to serve both handheld and console markets with one platform saddles the thing with the problems of both. Instead of dedicating all engineering and manufacturing costs towards power OR portability, they have to compromise on both.
If you treat it as a portable, you'll be irked not to have things like StreetPass or a decent battery life. Then, since the JoyCon come off it's a bit less sturdy. At least you can put your expensive system in front of you where hopefully thieves won't snatch it.
If you treat it as a regular console, you'll be irked that a lot of the money you spent was blown on a screen you'll never use. This was a major problem with Wii U because for instance, the revolutionary Wii U GamePad did very little for most games other than act as an inventory/map or TV off-screen. However, it's ~$100 to replace if it breaks and certain games (especially Ubisoft ones like Rayman Legends or Your Shape Fitness Evolved 2013) refuse to run without a revolutionary Wii U GamePad. They also put NFC chips in them, which NO ONE asked for. Since they had them they figured they might as well use them and came out with stupid plastic figures that contaminated most of their big titles in some way...and this didn't improve games the slightest but someone figured that would make them more money than spending money on a slightly better sound chip.
That's what disturbs me the most about Nintendo recently. They used to be legendary with customer support and offering good values for hardware and software. Now, it's all about money to a rather psychotic degree.
Don't get me wrong. When handled properly, LPCM is "real surround." It's all uncompressed channels, which is too much data to carry over an optical cable. This is why Dolby (lossy-compressed) formats exist. Audiophiles will say that LPCM is therefore the best, which is true, however unless you have golden ears, a super high-end sound system, and A-B testing, you will never notice. It's just a body part measuring contest. You know how most people game? Headphones or built-in speakers, neither of which have the kind of hardware you'd need to be able to tell apart lossy and lossless sounds! Not to mention you don't know what sound libraries the devs used in the first place.
HOWEVER, what irks me most about the two examples I originally cited are that Nintendo takes design limitations and pretends that they're for the benefit of the customers. They also said they went with resistive touch screens instead of capacitive to "minimize input lag." Oh, right, not because it was way cheaper.
Edit: I forgot to mention one thing. Everyone's focusing on Switch using carts instead of discs, which was kind of a given since it's a portable, unless they wanted to sink money into licensing a weird small disc or developing their own. However, with Wii U and 3DS, we've seen Nintendo DOES NOT want us to even have our save data. With disc-based systems starting from the Turbo CD, SegaCD on, you can copy your save files to some kind of backup device and move them to another system if something happens to your original system. With Wii U, those saves are LOCKED to that exact system and that format of the system, so if your system gets wiped, you can't even restore from a backup.
I'll bet you right now that Switch games will save to their carts and not allow you to copy that data unless you switch to the digital rental, as is done with 3DS games today. There are a few rare exceptions, but there's NO technical reason why you can't choose whether to save to cart or the SD card for every game. It's done for lock-in. The bottom line is money. :\