Because you don't need any checks. AFAIK, the PIN confirmation via chip takes at least a second. Online transactions take longer to confirm.

That's nicely solved with contactless. You get immediate confirmation that the card was accepted but the terminal still confirms online. The feedback comes 3-5 seconds later. That still allows the retailer to stop you if the card was declined but you can already use the time and don't have to wait until you can remove the card.

In addition to dx034’s answer, you put your card away right after swiping, but it’s still processing. With chip, you can’t remove it until it processes.