Why HiFi manufacturers don't make active crossovers anymore?

I agree whole heartedly that you can acquire a much better synergy of components by utilizing an active crossover!  Being a DIYer myself, my system is composed almost entirely of diy components and it sounds absolutely fabulous!  

My active crossover is a Sublime audio K231.  It is completely customizable and they are a great company to deal with.  Don't let the $500 price tag fool you, this is a top quality component!  

Would be happy to answer any questions in a PM, but don't want to get into the back and forth on this website!

The best crossover is a high grade capacitor to roll off the bass going into the mid/high.

One of my systems uses a pair of monoblocs to feed the mid and highs, and a separate set of monoblocs to feed the bass, with what is basically a fancy gain control in that end of things to allow matching of the outputs of the two different amps.

But not everyone wants to pay for two (or three or four) power amps instead of one and all the extra speaker cables (mine are triwired).

When you get into active crossovers you've added another electronic unit to the line that may or may not affect sound.

@mahlman

I use the 2x8 mini DSP. All filters are run at 24x96 and I have everything connected via balanced connections. The computer interface is simple and intuitive. Basic slopes are easy to create and load. On the 2x8 I added a selector knob which offers multiple options for source and many configurations for each source based on what you are listening to. For example I have a 5db increase on the subs for movies. Having the extra oomph is fun, makes friends jump out of their seats :) I also got the add on for SPDIF inputs which is lossless and seamless from my Mac Mini. 

I bought the board and case separately that they offer. It’s a very high quality piece of equipment. The flexibility is impressive.

The 2x4 only offers RCA connections and runs at 24x48. Depending on your application and size limitations I would spend a little more and go with the 2x8 option.

The best crossover is a high grade capacitor to roll off the bass going into the mid/high.

If you are going to go with multiple amps, or a satellite/sub, this is a really good compromise. No more parts, or power supplies, at the expense of only having a 6 db/octave rolloff.

If you use sealed (or plugged ported) speakers you can increase your speaker's dynamic range, improve your power handling somewhat as well.
I have a Luxman integrated that lets me separate the pre from the main amp and I'm thinking about doing exactly this.

Sorry, but I can't help but chuckle at the image of all these "audiophiles" wringing their hands over active crossovers being digital and too complicated, modern DSP crossovers do it all quick, clean and efficiently no matter what configuration you are trying, Bi, Tri, 2.1. Trust me, you won't hear any degradation from this unit and any bi-amp or tri-amp system will sing like never before. 
https://dbxpro.com/en/products/driverack-venu360
I was introduced to active crossovers (pre-digital) while working as a soundman for clubs and bands back in the early 90's and it allowed me to get the most out of whatever I had in the way of speakers and amps, which BTW is usually all run in mono. I took home a basic 2/3 way stereo X-over and started playing with it and was able to get some remarkable results with a little fine tuning. B/K Sonata 5ch amp worked great. Clarity and power like crazy, and solid thump out of subs instead of boom.
Today's technology makes it easy precise if you can get over your digi-fear.