A big factor that led to Nickelodeon's more strict scheduling and handling of shows towards the mid-2010's was when Disney Channel became the #1 kids network in 2012.

This ended Nick's 17 year record, and a challenge to retrieve and hold the title.

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Around this time Nickelodeon was experiencing a ratings decline for a number of factors (i.e. a lot of its shows on Netflix)

After 2012, Nickelodeon became even more strict with their shows and began airing more SpongeBob everyday to pick up those ratings, more every year.

Highlights from Disney Channel that helped achieve high ratings were the Wizards of Waverly Place finale, Let it Shine, Phineas and Ferb (who beat SpongeBob as the #1 kids' series), Good Luck Charlie and its then new hit sitcoms Jessie and Austin and Ally.

The strategy of only airing shows that receive high ratings and pushing the reruns and premieres off to Nicktoons has helped them regain and hold the title ever since, although it'w hirt their reputation:

Current weekly ratings:
#16 Nickelodeon (353K)
#27 Disney Channel (217K)

Aside from the dominating the boys/older kids' demographic, neither Nickelodeon nor Disney Channel have had to worry about Cartoon Network beating them in ratings.

CN has always been in third place within the kids' networks, rarely taking second place.