That's because laptops do not have the same programming that phones do.
Most phones (iPhones specifically) will charge themselves to 100% and then let the battery drain 1% and charge again. The phone is designed to cut the voltage and re initiate over time so as not to create heat stress on the battery. Leaving a phone plugged into the wall will barely impact its life span. Draining and recharging the battery from low percentages frequently is what kills phone batteries (below 80% far more voltage is expended to charge the phone faster, heating the battery. Above 80% the battery is charged with more care).
Laptops simply RUN. They don't ever stop. If you leave a laptop plugged in too often it will kill the battery far faster than you can imagine. In a lot of generic laptops you can remove the battery. That's the best thing you can do if you're going to leave it plugged in for the majority of its life.