If you are comfortable at operations you'll be fine. Some people are not good at ops so outsourcing the problem making the ops side someone else's issue can also be useful.
Self hosting will offer far more options when it comes to scaling and tweaking. Overall on bare hardware costs it's cheaper and faster although up front costs will be higher.
Kafka usecases are rarely elastic so don't gain that advantage in the cloud. Also Kafka's missing tierd storage makes it expensive if storing big volumes of data.
In practice, it’s better to offload things that are not core to what your company is making money on, until you hit constraint points from scaling. As one of the comments mentioned, at PB-scale processing, even bare metal may make sense. (But not always - one of my former employers went down this path early and ended up losing all productivity in R&D because of people fighting to keep that baremetal setup alive for months on end. This really hurt future revenue growth and distracted eng. leadership from key changes in their industry.)
Like with most complex questions, the immediate answer is “it depends”.