Why? Because that's what most beginner Texas Holdem strategy books tell them to do.
They've basically learned that one of the biggest mistakes a Texas Holdem player can make is playing too many starting hands - which is, of course, true
Unfortunately for them, they've taken it to the extreme and this is now a situation you can exploit.
So what's a winning strategy against these tight-passive opponents?
Here's an example:
The other day at UB.com I was playing some 50¢/$1 No Limit Hold em. The table was very tight and passive and most of the times I raised it up I won the pots uncontested.
When the game began, I was only raising with premium and sub-premium hands - say AA down to JTs. But when I didn't get any action and just raked in the blinds I realized I could widen my range significantly.
Think about the math here. If I raise to $3 each time and win two hands uncontested, I can play the third hand for free. Even if I'm re-raised and forced to fold every third hand, I still break even.
So I started raising with all suited hands, all connectors, all high cards - basically anything half decent (except bad aces, which are always a road to ruin when you hit an ace on the board.)
The interesting thing: my opponents couldn't (or wouldn't) fight back.
They obviously knew that the maniac raising 50% of the hands didn't have the goods all the time, but since playing only good starting hands is so deeply rooted in their minds they simply couldn't raise back with anything but absolute premium holdings.
If they had something like A-J, K-J or Q-T - which tight poker strategy says are not re-raising hands - they just called.
And when they call, I get the chance to hit something with my random hand. I probably won't go to the flop as a favorite, but even 7-5 off can hit a monster.
Another advantage with this strategy?
You'll get called a lot. Even if you play solidly on the flop, turn and river, your opponents will still see you as a donkey who bluffs all the time because of your loose pre-flop strategy.
But that isn't true of course. You're just taking advantage of other players' weak pre-flop play.
In short: When you play Texas Hold em poker and your opponents fold a lot pre-flop, you can create an image of being an idiot - for free!
When you then switch to a solid strategy on the flop, turn and river, your opponents will continue to see you as a big bluffer.
And they couldn't be more wrong.