Since this question is primarily opinion based - in my opinion :) - my answer will be primarily opinion based.
First, if there's one thing I've learned in the years I've worked in professional IT/security, it's this: It doesn't really matter if you agree or disagree with a company policy or if you think it's reasonable for them to encrypt traffic as a specific example; it's THEIR (insert company name here) company and they can enforce any policy they want so long as it doesn't break local, state, or federal law/regulation. If you don't like the policies then you have two choices: suck it up and continue to work there, or find another employer; it's really that simple.
Now on to my personal opinion of the matter. I don't think it's a question of whether it's reasonable to encrypt all traffic, even internally, but it's more of a question of why would your leadership want to do this. I work for a federal agency that has several enclaves (we'll call them islands), one of which deals with SCADA and Industrial Control Systems (ICS). These ICS enclaves/islands have way more sensitive data than the general enclave that almost all other users are on and in my opinion would be justified encrypting all traffic. This could help against potential attackers that would try sniffing the network as an example for any helpful information they could obtain. It could also help prevent a myriad of other things, but when it comes down to it there is a good business case/justification for this. The business case/justification is that if an attacker gained access to the regular non-ICS/SCADA enclave there isn't much that they could do to damage the systems out in the field controlling important infrastructure. If they, on the other hand, gained access to SCADA/ICS data from something as simple as a network protocol analyzer they'd have the keys to the kingdom and could take down some seriously critical infrastructure that would affection a lot of people. That right there is justification to be at least a little paranoid as well as more cautious and take measures such as encrypting all of the traffic internally and externally. Not all networks would have a good justification for encrypting all traffic.
To answer your specific question, I do think it should depend on the network segment as you've put it, however it may be easier operationally to encrypt all traffic rather than trying to cut out certain areas to encrypt vs leaving others unencrypted. But, without knowing your company's leadership I can't say why they'd want to do this across the board.