It never was part of TWC's starter cable package, but probablly the "standard cable" tier..
Basic cable went away 5 or more years ago and got split in the above 2 tiers.
I seem to remember seeing Nick on smart tv's as an ala carte channel.
The entire time I have lived in my home I have had Nickelodeon. This is the primary channel watched in my household. Today, while switching from TWC to Spectrum, we were told Nickelodeon is not on the "basic channel package." I think this is atrocious, especially since I have had this channel with TWC since I can remember. Please put Nickelodeon on the basic channel package. I really don't want to have to switch my cable and internet provider.
If you are paying retail rates for video, then Spectrum Select ($64.99) + the digi-tier that contains Nickelodeon ($12.00; Total = $76.99) is cheaper than the rate for TWC's "Standard" tier ($78.99). In addition, Spectrum STB fee is $5, where TWC's is $11.75. So you come out ahead even if you have to buy an extra layer of programming.
Do realize that Viacom (the owners of Nick) had to allow them to move the channel to a higher tier...