I assume that that Sojourner Mars rover received its initial R&D funding
in 1994.

But there was no Mars rover project funding between 1976-1994.

So why DIDN'T the taxpayer provide funds for a Mars rover after the Vikings landed
on Mars in 1976?...

The answer?...It wasn't so much the billion/two-billion dollar price tag originally quoted in the seventies and eighties, as it was that the millions and tens of millions of taxpayers weren't particularily interested in sending a wheeled science package to Mars to do more geology back then.
After the Vikings failed to find life on Mars, the general public's interest in sending a
follow up [roving] mission to Mars faded away for a generation.
We here on HabitableZone ARE NOT a fair representation of the general public because
of our hardcore [even fanatical] interest in space travel and the sciences.

The general public has a passing interest in science discoveries and space travel, but by no stretch of the imagination are most 200,000,000 US taxpayers hardcore space travel enthusiasts
or science fans...They love the beautiful Cassini and HST images posted on the net or on CNN,
and they get excited [for a time] about possible life found in a martian meteorites [1996],
but such interest among taxpayers quickly fades. The general public is fickle...