If there was massive voter fraud as Trump & his supporters claim, why was Biden the only beneficiary & not the Senate as well?

You're exactly right! Who steals the golden egg when the goose that lays it is sitting right there! 

Elections are all about how the taxpayers dollars will be spent, and Congress holds the purse strings. 

They weren't looking at loosing anything after they tampered with the process.

Less chance of being called out because of increase in voter turnout in state when those fraud ballots hit. Longtime mob boss in Philadelphia is willing to roll over on Biden campaign in exchange for being expunged of crimes over the last two decades for 300k fraud ballots at $10 a pop. $3 MILLION. Number of down ticket votes in battleground states are normal for Republican but highly irregular for Democrats. Yea, nothing to see here  lol

And Democrat majority House gonna pass any legislation for Senate to vote on? As if

Well we already have a series of grounds including hundreds of affidavits, cell phone cams catching ballot altering, rerunning, and wheeled in suitcases and coolers of more ballots.  We have images of Trump ballots in the trash by the thousands, we have large batches of ballots where the signature appears to be from the same person.

So there is reason to investigate.  Why didn't the senate get rigged too?  I have no clue, but it doesn't eliminate the evidence shown for the altering of the presidential race

Not every seat in the Senate was up for election this year. 

Exactly. Conspiracy theories can be very flexible

They're claiming that Democrats purposely lost the Senate as to make it not "obvious" that there was fraud.  No, it doesn't make any sense.

Some are even claiming that Democrats committed fraud in 2016 but that they didn't commit ENOUGH fraud so Trump still won.  They don't live in reality