EDIT: I feel compelled to explicitly say that this was a mind-bogglingly stupid thing to do, and there is almost no way to justify it. I'm just curious what they thought they were accomplishing.
"Creating a new cryptographic hash function is no trivial undertaking, even when it is being built on preexisting world class standards. “Don’t roll your own crypto” is a compulsory uttered mantra that serves as a good guiding principle for 99.9% of projects, but there are exceptions to the rule. When spearheading technology for a new paradigm this statement is no longer axiomatic. Progress must march on."
"Because we needed an efficient hash function for IoT and the future of ternary computing (memristors, spintronics, optical computing and the trend in Artificial Neural Networks)
This has been known since before we even began the project. I spoke with the Keccak team about this all the way back in early 2015 before a code of IOTA was written"
Their motivation is really being able to claim an "improved" and "different" cryptocurrency to an audience of promoters, investors and speculators.