You badly underestimate the percentage of hands on which game can be bid and made. At an average of 7 or so minutes per hand, roughly the tournament standard, one can easily complete 24 or more hands in about 3 hours. Of those, upwards of a third have game biddable and makeable (or an equivalent penalty if the opponents over compete). That's easily 3 or even 4 rubbers in an afternoon or evening. I've seen 7 board Swiss team matches with 5 games bid and made between the two directions.
If we were to make a comparison to tennis, specifically men's tennis, then a rubber corresponds to a set rather than to a match. Bests of five sets can generally be completed in 3 to 5 hours; and the same could be expected from playing 5 rubbers and computing total score.
Update, responding to comment below from OP
Non-Vulnerable: down 3 doubled is a set of 500; the same as a slow rubber bonus.
Vulnerable: down 3 doubled is a set of 800, 100 greater than a fast rubber bonus.
Expert players will routinely defend against weak players 1 or more tricks better than they should, due to both giving away less and to taking full and prompt advantage of openings from their opponents.
Down 3, doubled, is the score one is attempting to avoid when competing, based on distributional values rather than high card strength, against opponents with moderately strong hands. But weak players routinely fail to do so - because they are weak players. So an ostensibly correct sacrifice becomes an incorrect one from an inability to play the cards to full advantage.
Strong players prey on this in money games (at stakes ranging upwards from 5¢/point) by sitting on a vulnerable part score and collecting penalties of 300, 500, 800 and more - every hand rather than every 4th or 5th hand.
Now look at the score card. My expert partner and I in the first five hands of a rubber won a game, lost a game, and collected a part score. Then we collected 1100 points in penalties over the next 4 hands before conceding a slow rubber bonus. We're up 600 points even though you won the rubber; and we're only an hour into a 3-4 hour session of bridge.
Later, we will bid and make the slam we're dealt for an additional 500 or 750 bonus, while you unluckily fail in the one you were dealt for another 800+ to us, due to mis guessing a finesse (that could have been avoided with a throw-in).
At the end of the session you have "won" 3 of the 4 completed rubbers - and at 5¢/point are still each paying up $100 to us.
Rubber bridge (or, for that matter, Chicago with part scores) is a vicious game not for the faint of heart. If you're not at least the second best player at the table - I advise moving down a table and letting another sucker in.
Now you ask: Why would anyone do that?
Simple? They are paying for lessons in how to become a better player. If one is patient, courteous, and polite; and both willing and able to pitch advice in a kind tone, between hands, and only when solicited, there is no shortage of opponents.
As to how I spent my winnings - I invested them in becoming a better backgammon player, under a similar understanding. ;-)