It's a combination of several factors others here pointed out.

Beer is a pretty decent diuretic (makes you pee).

It's practice/addiction/tolerance to be able to drink any amount of alcohol, but beer is weaker than spirits or wine, so you can filter it quicker.

Finally, beer is mostly water. If you're constantly drinking and peeing it out, you can go through it quite quickly (like water) while your system is filtering.

The general rule of thumb is 1 drink/hr filtration. Be that a pint, a glass of wine, or a shot of hard liquor, the filtration rate is roughly equal. Food alters this rate too. Pizza is paired well with beer because it's highly filling and stays digesting for a long time compared to something better for the body, like a salad. So on a full stomach of pizza, you can drink more than an empty stomach, but not suffer from the same intoxication level.

Beer also has a sugar content, but nothing like the orange juice you mentioned. It has some sodium, but not a ton, like soda, and is one reason why water is toxic if you have too much, causes sodium deficiency.

I say this as an avid drinker of all adult beverages other than tequila.