Have you ever noticed books trying to bait you into taking a parlay?
Example:
Team 1: -1000
Team 2: -2000
But parlayed you would get -500.
Or limit would be 10000 to win 1000, 20000 to win 1000
But parlayed, you could risk enough to win 5000 (not 2000)
There is nothing wrong with parlays as long as you are not getting shorted on the odds.
They are a great way to reduce risk and increase rewards. There are advantages to parlays in money management as well.
Sure there are parlay cards, and "odds boosters" on short odd same game parlays, but truthfully the sportsbooks, through all the years, never really pushed or advertised the two pick parlay.
There's a reason for that beyond the correlated parlay factors.