Bay Area trains and buses are crowded places nowadays, as expensive gas and jam-packed freeways push more commuters onto transit in record-breaking waves. Many casual riders discovered that first hand Wednesday, when more people packed onto BART and Caltrain than in any day in history after both operators beefed up service for the World Series parade.

Riders tired of packing into crowded trains and frustrated drivers wanting public transit to make room for them may be asking: Why don’t train and bus operators always run more service like that?

The “if you build it, they will come” theory, known in the transportation world as “induced demand,” has proved true time and again with expanded freeways, as new lanes typically attract more drivers lured by the potential for extra room.

Unfortunately for transit lovers, it’s not that simple to do the same for trains and buses, mainly because more service typically means more red ink.

“Public transit in the United States of America was not something that was started to make money,” said Mary Currie, spokeswoman for the district that operates Golden Gate Transit. “And it doesn’t.”

Trains and buses that are packed to the brim can break even financially, and during special occasions like the Oct. 5 to 7 weekend of special events that coincided with Fleet Week, transit operators can even make a small profit.

But adding more service every day would mean an even higher taxpayer subsidy for a region that’s already one of the most heavily taxed places in the country. Officials say raising fares won’t work, either — it won’t pencil out unless fares double, triple or more, and then many people would stop riding.

What’s more, most transit agencies simply don’t have what it takes to operate beefed-up service all the time.

Consider BART, which maxed out Wednesday by running rush-hour service all day and saw its rider count surge 40 percent to 568,061, a one-day record. But to do it, BART had to use 90 percent of its 40-year-old train cars and call in more than 100 extra employees for overtime.

“A good analogy might be (this): From time to time you might be able to work a 16- or 18-hour day but you simply can’t do that day after day,” said BART spokesman Jim Allison. “It’s not something we could do for days and weeks on end, not with the equipment we have right now.”

Still, the beefed-up service and rider numbers that accompanied the San Francisco Giants parade and Halloween revelry proved that people who don’t usually ride transit at least have the desire to try it. On Wednesday:

Caltrain added 14 trains and nearly doubled its daily rider count to about 90,000, breaking the previous record of 80,000.

San Francisco Muni light rail added six trains and traffic surged 55 percent, with more riders than during the city’s Super Bowl and World Series parades in 1988, 1989 and 2010.