Some people are passionate about being professional in the sense of doing things competently and expertly. Cuteness is inherently a mental distraction from what you really care about in the craft, which is why it appears tonally inappropriate. The desire to add some sort of cuteness is taken as an indication that the person apparently doesn’t derive enough joy from the workmanship itself. In other words, a lack of caring about and being fulfilled by the actual work, so that you need to add something “fun” on top.