The fact it'll work on as many devices as possible.
And if you add a Checkbox "Use DLNA compliant profile" in Prefs, Serviio will work with exact same number of DLNA devices, plus a large number of UpNP higher end devices, thus making Sergiio audience twice bigger with a little effort (just using UpNP engine).

I think, you incorrectly interpret, what DLNA Compliant means. Its easier to understand if you look at DLNA Certificates for various products on DLNA site. This simply means that given device is able to communicate with other devices via DLNA protocol, when they need it. It does not mean, the device should NOT be able to communicate with other devices via UpNP protocol. For example, my player's Certificate says:
"MEDIA FORMAT INTEROPERABILITY
This product has been tested for compliance and interoperability for the
following media profiles and capabilities
Device Class: DMP
----------------------
Audio LPCM Play / Stop Capable"
That's it! This means, if a low hardware device gets connected, the player can play media from it, if the media is in Mono or Stereo LPCM format as per DLNA Guidelines. However it doesn't demand, if a high end device is connected, the player must NOT play any other format from it apart from Mono or Stereo. The player will simply use UpNP protocol to communicate with such device instead of restrictive DLNA. So, DLNA does not prohibit for compliant devices to also support other protocols.
DLNA compliant mode is and should be offered as a
selectable option, but of course Sony can (illegally) offer incentives to developers who purposely remove all other mods of operation except DLNA. Its a lot cheaper than bribe lawmakers in every country around the world to frozen DVD age forever, and they can hide such activity behind "interoperability" scam, while if such law is introduced it will result in public outrage.
I agree that device manufacturers should also offer more advanced streaming servers, because they get paid. However, its a common knowledge that device hardware makers are far less able to concentrate resources and staff on generic PC software, even if they wanted to.