From my quick survey of the charts in 1991 versus now, I would say that the guitar bands overall have declined. In 1991, you had bands like harder rock bands like Van Halen, Metallica, Skid Row, and Guns N' Roses on the charts along with some more "alternative" bands (REM, U2) and a little dose of country (Garth Brooks).

Now? Alternative bands (now labeled "indie") are increasingly all electronic -- how much guitar is in the Twenty One Pilots album currently on the charts, for instance? Hard rock is still on the charts (Avenged Sevenfold and In Flames among others have albums on the charts) but it's a shade less prominent. Country is probably the one genre in the US which is both very popular and has prominent guitar, but even that is more electronic than it used to be -- just listen to all the synth in certain Keith Urban tracks.

The synthesizer is now what rules pop music these days, in my opinion. Even hip hop, which always used electronics as long as I'm aware, reflects some of this change (a lot of hip-hop has abandoned samples in favor of pure synthesizer tracks).

This change makes sense to me. As long as you have a computer, you can nowadays download an entire studio for practically pennies, and start creating satisfactory loops fairly quickly. A guitar most likely will cost more and definitely will take a lot more practice to get to that "instant gratification" point.