You could argue that the Virtual Boy was an attempt at replacing the Game Boy though so really it was only on the market for 6 years before a successor came along
But yeah, 8 years of the Switch is crazy especially considering that there hasn't really been a downturn in success in all that time. The Game Boy ebbed and flowed through its life before getting a huge late boost when Pokemon came out but the Switch has really only started losing pace in these last few months - they have certainly done a much better job at its end of life than they did with the Wii U, Wii, Gamecube and N64.
Also we're now less than a calendar month out from the Switch 2 Direct but I'm sure the original Switch will still have a presence in the market for the next 18 months or so