The main difference between pilot logbooks and aircraft logbooks, of course, is that aircraft logbooks transfer to a new person upon sale of the aircraft. The second main difference is that entries in pilot logbooks are generally made by one person, i.e. you, with occasional others (a CFI), but even that is often done with you physically there.
Those fundamental differences are the key, though. Physical aircraft logbooks are really easy to transfer upon sale - you place them on the back seat, done. Electronic logbooks would have to have a login/permissions issue, maybe the new owner prefers a different software package so it would have to be converted, and of course the new owner would have to want to use electronic logbooks in the first place.
And as for making entries, the mechanic would have to be on board with whatever system you want to use. Change mechanics, maybe they use a different electronic system. Get your alternator replaced at a distant airport while on a trip, that mechanic would have to be up to speed with your logbook system. And if they're not, and give you a sticker for your logbook, what do you do?
None of these issues are unsolvable, of course. But especially for light GA, there's a whole lot of inertia in the aviation maintenance world, and paper logbooks are probably just seen as far easier for the vast majority of day-to-day maintenance interactions.
In the corporate or 135 world, of course, it's likely a different story.