Graphic Equalizers, aside from misuse issues, generally fell into two categories.
The first, were conventional branded consumer electronics models with marginal specifications. Generally just incorporating the EQ with all levels neutral immediately added noise, phase shifts (destroys imaging), and overall not HiFi quality. Those with adequate performance were costly.
The second were Pro Audio versions from the likes of UREI, etc. They were of excellent SQ, but were costly, in some cases single channel (needed two for stereo) and so on. They are gone because analog equalization is no longer used in the Pro space, replaced entirely by digital filters in Digital Audio Workstations (DAWs) or even simple music playback software.
Also, with the death of magnetic tape recorders/players, the circuit used by analog EQs began disappearing from audio gear (sometimes renamed "processor loop" or similar on face plates). So there is no practical way to hook them up, except between a preamp and power amp, which creates SQ issues (your preamp's overload margin and all other performance capability is now limited effectively to the Equalizer's).
Finally, the best Equalization was not via a Graphic EQ but a Parametric EQ. The replacement of the "bling" sliders with four of five knobs and switches didn't offer the same look in the rack that some buyers wanted.
All in all, most people are happy to see them go, and Pro Users are overjoyed. Digital Signal Processing (DSP) does a much better job of actually effective equalization.
If you really want one, the best quality Pro Units are widely available used for give-away prices, since they no longer have any Earthly Use. Conversely, in order to fill out the racks of collectors who want every component in a system series, the quality branded units are quite expensive.
