The solution _is_ running HTTPS internally. But as an application developer, do you want to manage certificates? Do you want to make sure you're using the "correct" TLS versions and that your app can talk to other TLS versions? What happens when team Z deploys their legacy Java app that doesn't? Where are you getting your certificates from?
All of these go away with a service mesh and sidecar model where the everything is encrypted for you and certificates are completely managed by the service mesh. No need to roll your own PKI. Your app only needs to speak plain HTTP and from it's perspective every other app is also just speaking plain HTTP, no TLS in sight. It makes developers' jobs a lot easier, only concentrating on shipping features vs. wrangling with TLS.
Saying all of that, you could just roll your own fine. Depending on the competency of your company.
All of these go away with a service mesh and sidecar model where the everything is encrypted for you and certificates are completely managed by the service mesh. No need to roll your own PKI. Your app only needs to speak plain HTTP and from it's perspective every other app is also just speaking plain HTTP, no TLS in sight. It makes developers' jobs a lot easier, only concentrating on shipping features vs. wrangling with TLS.
Saying all of that, you could just roll your own fine. Depending on the competency of your company.