My first synth was a CZ-5000, basically two CZ-101s in a single unit with 61 full size keys and 8-part multitimbral plus an 8-track linear sequencer...a workstation in today's terminology. It was very usable, much simpler to operate than a CZ-101 in multi mode. I used workstations as my prime synth right up until I sold of all my hardware at the end of 2017.
Multitimbral polysynths made sense to me because they were economical. The CZ-5000 could do the work of multiple instruments (as many as 8) and a sequencer (in those days, a relatively expensive hardware box). Within a few years, workstations came with multiple FX processors, too. In 2005, I purchased a Motif ES6...16 parts, 128 voices, 18 FX processors, internal mixer with EQ and send busses...and replaced four MIDI instruments, five FX processors, a mixer and a patchbay.
As others have noted, Reason itself began as a software implementation of a workstation....multitimbral, sequencing and effects in one device. It wasn't really a DAW in the early days since it didn't record audio, output MIDI or support plugins...it was a standalone application that accepted MIDI input and supported multiple channels of audio output. Within a year, I bought Reason 2.5, slaved to the Motif as an expansion device and ran the output of both into my hardware multitrack recorder.
Since Kontakt has been mentioned, keep in mind that Kontakt is not just a plugin, it's also a standalone instrument (I think Massive X is the sole NI instrument that is only a plugin...even Komplete Kontrol runs standalone) that can be run outside of a DAW. This is also true of IK's SampleTank, Arturia's V-Collection and Korg's Legacy Collection. It makes perfect sense for these to be multitimbral.
No DAW handles multitimbral plugins well because of the inconvenience of routing multiple MIDI channels into the plugin and routing multiple audio outputs. In every DAW I've used to date a multitimbral plugin like Kontakt or SampleTank requires setting up 16 MIDI tracks and 16 audio tracks. In many usage models, it's simpler to instantiate multiple instances of the plugin. The orchestral library case is one of the exceptions.