A lot of singers want to have raps in their song, but they can't rap themselves. Or they want to credit the producer of the track.
Plus, a lot of people are more generous with crediting today. On Party Rock Anthem, maybe a few decades ago, the exact song would've just been credited to LMFAO. Lauren Bennett's vocals would've been left uncredited, and the producer GoonRock would not have been credited. Or on Give Me Everything, if released in the 70's or something would've probably left Nayer as uncredited background vocals and not credited the producer.
It is a bit of a trend, but on the other hand, a lot of the "solo" songs from the past would probably have a list of features added to the end if they were released today, just because people are more liberal with crediting now.
With the popularity of dance music at the moment, the DJs are often getting credited. And collaborations have always been a big part of urban music for decades, so since urban music in the mainstream has exploded in the past 10 years, it''s only natural you'll see more collaborations in the chart, and the collaboration culture of urban music has passed over to pop music now aswell.