Hello Jmir,
The SDKs were developed in the first place by freescale and were adapted to the LPC parts after the merger. That should be the reason that Kinetis devices are more widely supported by the SDKs.
I think both lines are in product care and maintenance now and will not be developed much further (meaning no new part, but the SDK is still developed). NXP focus is on the new lines now, I guess. If I would start a new development, I would use the K32L-Line for smaller projects and the iMXRT-Series for anything which has higher requirements