Keep doodling is easy on Android, since you draw right on the screen with your finger or a stylus. Though it does work with a mouse or touchpad, it's less logical on a laptop, unless you have one with a touchscreen. Since Chrome apps are primarily geared to Chromebook owners (Google is phasing out Chrome apps on Windows and Mac), the Keep's drawing feature perhaps points to a more touchscreen-oriented future for Chromebook. Samsung, for one, is rumored to be releasing a hybrid, stylus-equipped Chromebook Pro for around $500.
Tablet sales down across the board, with the notable exception of hybrid models that can double as a PC, like Microsoft's Surface or the iPad Pro. It makes a lot of sense for Google to make a stronger push into the hybrid PC game, where it can perhaps offer a better price-point than its rivals.
The search giant has already started by porting tablet-based Android apps to Chrome OS, giving users of select models more to choose from. By making its core Chrome apps more touchscreen friendly, it might motivate its hardware partners to create hardware to match. To get the Keep's drawing tools on Windows, Mac or ChromeOS, just go to the Chrome Web Store and search for "Keep" (or click here). As mentioned, don't get to attached to the function on Windows or Mac, though.