Google changed the way Chrome handles tabs in Android Lollipop. By default, tabs no longer live within Chrome like they do on the desktop.
Instead, when you hit the multitasking button you’ll see each tab parceled out as if it were an individual app. The advantage is that it may be easier to find that last tab you were looking at because this view puts the site’s icon and name at the top of the card.
If developers want to get really wild they can customize the color of the top bar so it stands out amidst the other apps.
However, if you long for the old way of doing things, open Chrome and head to Settings > Merge tabs and apps. Then just flip the feature off. You’ll get a notice that the tabs will move to the tab switcher inside of Chrome. This also re-enables the ability to close all your tabs at once by going to Settings > Close all tabs.