My guess is that they mean relative to capacity. If the card is simply the same speed at a card 1/4 the capacity, that means you can read out only 1/4 as large part of the unit per unit of time.
Apart from the thermal throttling suggested elsewhere, there's also the bus speed, as well as the controller on the card. It's possible they could speed it up, but it's just as likely that they've just added 4x the same flash with a controller with the same read/write performance.
SD cards != SSDs. The applications they are used in tends to be more limited by capacity than speed, and they evolve accordingly.
Apart from the thermal throttling suggested elsewhere, there's also the bus speed, as well as the controller on the card. It's possible they could speed it up, but it's just as likely that they've just added 4x the same flash with a controller with the same read/write performance.
SD cards != SSDs. The applications they are used in tends to be more limited by capacity than speed, and they evolve accordingly.