Some games are still released with a proper full cartridge, but the key cards are chosen increasingly frequently by devs. I've heard the I/O bandwidth on the cartridges is just not enough for modern games with huge files, so they deliberately choose the key cards to force players to play off the faster internal storage. At first, I found it befuddling that Nintendo wouldn't do something about that before the hardware got finalized, but now, in light of Sony pushing full digital, I suspect it was a deliberate choice to start prepping customers for a strictly digital future.