I got into Arduino-controlled stuff a couple years back, because I had a need to build some machines that would benefit from being digitally-controlled. I picked Arduinos for a few reasons:
1--they didn't need a separate programmer at all, just a USB cord. This makes them a lot more convenient for newbies to experiment with.
2--They were available cheap. The Italian ones cost some money but the copies on the direct-orient sites are available very cheap. And these are not just chips, but ready-to-use boards. Unos for $5, Megas for $9, Dues (ARM cpus!) for $15 and the shipping is free. They cost even less if you don't need the USB cable.
3--I had a need for such a device. Ever see where people post "I bought this Arduino (or rPi), what can I do with it?" ***
I'll never choose a PIC for hobby use, nor would I recommend them. Arduinos totally beat them on both cost and convenience.
***(By the by, the only two things that can be built with a rPi are (1) a MAME cabinet, and (2) a home file server. Any other claims are merely gratuitous falsifications)