Why is my laptop slower than a desktop with the same specifications?

The specification sheet is comparing names rather than capabilities. Processors sold for laptops and desktops with similar model numbers frequently have very different power and cooling budgets, and sustained performance follows the cooling rather than the name.

A desktop processor may be permitted to draw several times the power of its laptop equivalent, and a desktop has room for a large heatsink and unrestricted airflow. A thin laptop has neither. The consequence is that a laptop can match desktop performance briefly, then reduce its clock speed as it heats up. This is thermal throttling, and it is why benchmark results from a short test overstate what a laptop delivers during sustained work such as video export or compilation.

The same applies to graphics. Mobile graphics chips carrying the same name as desktop parts are configured for far lower power, and the difference between two laptops with the identical chip can itself be substantial depending on how much power the manufacturer allows.

Storage and memory add further variation. Laptop memory often runs at lower speeds, and thin machines sometimes use narrower storage connections.

There are practical things that help. Ensuring the machine is on a hard surface rather than a soft one, keeping vents and the internal heatsink free of dust, and selecting a performance power profile rather than a balanced one all recover real throughput. A cooling stand helps more than it sounds like it should on machines that draw air from underneath.

When buying, sustained performance reviews are far more informative than specification comparisons, because they measure what the cooling design actually permits rather than what the chip is nominally capable of.