The answer is never "engineers are lazy". The answer is, the company doesn't give a flying fuck about this problem and will actually prevent engineers from working on solving it, because they can sell you a TV perfectly well with this problem still present, and there's other work for engineers that makes TVs easier to sell than actually delivering a quality product.
Decrypting and demodulating have be as fast as the data is coming, otherwise the delay would grow until you never saw the end of the show. So that's not the reason either.
Your TV doesn't have the information it needs to start displaying MPEG-2+ATSC A/53 video for as long as 700ms. It needs to buffer quite a bit of timing information and at least an I-picture frame before it can start displaying anything: http://www.bretl.com/mpeghtml/startbuf.HTM
Not only that - the overall standard has tight timing tolerances to keep video arriving at the encoder/transmitter in-sync with audio/video leaving the decoder in your TV. It's not like MP3 streaming where every client has its own buffer size and time to start playing depending on network conditions, bitrate, etc.
Having a reliable buffering process to keep receivers in-sync is a feature, not a bug.
You're sure this is engineering laziness? How much extra would you pay for a TV with faster channel changing?
Simple solution: just put 10x decoders/tuners for most recently used channels. I don't think it's really an engineering problem but more about cost-effectiviness, i.e. not enough consumers are willing to pay the premium.
However, even if the read-ahead tuner was perfectly predictive you'd still need to flip through channels fairly slowly, otherwise you'll outrun it - about a second a channel.
If your answer to the question "why can't a billion dollar industry provide me with instantaneous channel switching?" is "because they are lazy", you are severely misguided (at the very least!). There are hundreds of extremely talented engineers working full-time on these problems. If the solution were as easy as you propose, the issues would be solved.
> zero boot time
That's not going to happen, ever, but I'll assume you meant "faster" boot times.
Probably. Keep in mind that your average set-top box likely goes through a more complex secure boot process than most electronic devices you would ever interact with. Why? Because if people can run arbitrary firmware on a set-top box, your cable company would lose a shit ton of money.
> instantaneous channel switching
You are bound by the latency required to demodulate a signal being broadcast from some satellite ~30,000 km away from the receiver, decrypt the resulting stream, and finally decode it, all on the fly so you get a nice, continuous, stutter-free full HD broadcast.
I am no expert, so there is probably way more stuff happening behind the scene that someone else could probably shed light on. The point of my comment was to demonstrate that things can sometimes be more complicated than they seem at first glance.