F-zero has always sold well.
F-Zero (SNES): 2.85 million
F-Zero X (N64): 1.10 million
F-Zero Maximum Velocity (GBA): 1.05 million
F-Zero GX (NGC): 1.8 million (according to Nagoshi, 2018 interview)
If you include Climax and the VC figures for F-Zero SNES, the franchise has sold more than 7 million units, an extremely respectable figure, especially given that 2 of the 4 consoles it graced had a smallish user base. It sold more than Fire Emblem (excluding all post-2004 releases, so that we can compare similar time frames), Kid Icarus, Pikmin and Xenoblade, all active franchises.
There's no reason whatsoever for Nintendo to hold on to the franchise besides the fact that all of its consoles since 2006 have been underpowered compared to the competition, and visual oomph was always a huge part of F-Zero, ever since it came out blowing people's minds with Mode7.
Nagoshi and SEGA have said more than once they'd happily developed another title if Nintendo would let them.
It’s actually 1.5, across three regions, and you left out the two GBA successors that apparently seem to have done abysmally.
That isn’t well, by today’s standards, which is what’s being discussed. That’s additionally questionable by 2003 standards as well, and things haven’t gotten any better for the genre, with a depression all around, and even the closure of long-time favorite Psynosis.
Why should Nintendo invest their top-tier talent or money in such a small/risky return, with a much, much bigger budget to meet today’s visual standards, when they could make something that sells 10-20+ million, like much of their output today?
There isn’t a single business reason.
With Pikmin, it’s the boss’ pet project, and still hasn’t seen a new, real installment in seven years, as other Nintendo series lap it with multiple sequels. A dual screen sidescroller, at less than indie level, that cost figurative pennies to put together, and continued reheating of ready-made Wii U leftovers hardly qualify.
Kid Icarus is an abandoned modern one-off, and hasn’t seen an installment for eight years.
Xenoblade does better and better with every installment, trending upwards, despite being handicapped by release shenanigans for the first, the literal Wii U for the second, and it’s niche nature, with the latest remake selling a million in just one month. Does F-Zero have that momentum or potential? Or would it be very likely to sell worse than the 2003 incarnation, looking at the market around this genre?
Additionally, do you think that after 17 years, the Switch couldn’t output a game that lived up to F-Zero standards?