Has Apple ever rolled out MacBooks with FileVault enabled by default? If yes, which version(s)? If no, is there a reason why they wouldn't?
Apple has not, to my knowledge and research, ever released a machine with encryption turned on by default.
Even with APFS that natively supports encryption* (meaning it's baked into the cake and not just another layer on top), encryption has three options:
- no encryption
- single key encryption
- multi key encryption
This is something the user must select. Why Apple chose to go this way is something that only Apple knows, but it's evident that they wanted to give the option to the end user (or at least to the people deploying the Macs to the end users).
* 9to5Mac.com: Apple File System (APFS) announced for 2017, scales ‘from Apple Watch to Mac Pro’ and focuses on encryption
I want to add a caveat to @Allan answer.
No Mac ships with encryption on. However, on newer Macs with the T2 coprocessor, the macs are in fact encrypted from the get-go. However, everything has access to the decryption keys. When you choose to enable FileVault 2 the Mac wraps the keys in a secondary layer of encryption basically instantly activating the encryption. So although it is not turned on by default, the drive is in fact encrypted and upon activation, the partition is instantly encrypted.
I just received a new MacBook Pro (11-26-18) and Firevault was NOT on by default. I had to manually turn it on.
They have, since 10.10, marked the FileVault encryption options as enabled by default in the new Mac setup. This is optional, but as the options are checked as on by default, this makes it an opt-out feature that a user has to consciously uncheck (and most people go with the default).