Surely it is unrealistic to think that any one manufacturer can be good at everything?
One that did come close is Quad, who started making valve and solid state amplifiers after WW2, then added world-class electrostatic loudspeakers (still heavily based on electronics). When they moved towards the source components, the best they could do was modify a Philips CD transport. Never touched turntables.
Under their new owners, they have gone very down-market in my opinion with dynamic speakers and some very 'ordinary' amplifiers in the range.
Staying British, KEF makes class-leading speakers in several categories, but has never made separate amplifiers or source components. Their active speakers do have internal amplification but that's where it stops, at least for now.
Then I thought of Linn, who kicked off with a turntable, added speakers and who used to be frequently partnered with Naim amplification. After years of decrying digital, they include CD players and streamers. I have just discovered they now also make power amplifiers and sell cables so they could be a one-stop shop after all.
One thing I am sure of - no one dealer has ever stocked all the components I use!