Ask Electronics

You need to control the current going through the LED, either by wasting it as heat (resistor or linear controller) or via switching power supply mechanisms.

Non-intelligent LED strips (where the whole strip is the same color, as opposed to the intelligent kind where each LED can be a different color) are generally not using a resistor per LED because you can use a row of LEDs in series with a single resistor. Generally there's a marking to designate where you can cut such that they've got several LEDs per resistor because each LED is going to be somewhere in the 2-3V range, depending on color.

Strips are a design compromise built around convenience, of course. But there's a lot of engineering compromises here because the switching power supply is going to burn up some energy running things as well.

Manufacturers of finished LED products do make bright LEDs frequently by making a series-parallel array of LED chips on a single substrate such that they've pre-selected similar LEDs. But if you are building your own strips, you can use a constant-current switching supply to run a series of LEDs off of a relatively high voltage, somewhere in the 24v to 48v range, where you'd want to select for a relatively bright individual LED so you don't need to make a bunch of the constant-current switching power supplies.