Yeah, except they write 2-5 times more code in Java, than they would in Kotlin. I think it's unprofessional to reject a new language, that will make code smaller and easier to understand, just because somebody is afraid to step out of his comfort zone for a moment, and not because of some potential real problems.
I think you can justify anything with that stupid line of thinking: "I don't use for-loops, because a while-loop can do the same, and it's too hard for me to learn it." Sounds the same to me. Learning Kotlin is a must for any Android developer, unless he really likes to give handjobs to the Java compiler: "Oh, let my type the name of the type twice, even if it's quite long for clarity and you know it already from the right hand of the assignment. You want me to write 23 lines of boilerplate in a separate file for a POJO with 2 fields? Oh, you dirty boy!"