Is there some legal restriction against it? This seems to be a rather glaring omission in the market, as the cable company will gladly rent you a DVR that lets you skip through commercials and record any channel/show you have a subscription for, but both streaming services and hardware manufacturers seem to think it is okay to go back to the bad old days of broadcast TV where you had to be present at the appointed time to watch a show and/or sit through all the commercials (a common requirement for VOD - no FF'ing allowed). This situation is even more confounding to me since I can buy a DVR to record OTA signals - ie, free ones - and then skip through the commercials with impunity, while with streaming services I basically have to pay to watch commercials!?
Now I realize that some streaming services offer DVR functionality, but said functionality is entirely at the mercy of their terms of service and invariably cloud-based with capricious/one-size-fits-all specs or bizarre restrictions. If I want to record an entire season of Archer or The Expanse before watching it then I better not use PlayStation Vue as it only stores recordings for 28 days. If I don't want a show I thought was recorded to get substituted with a VOD version which then forces me to sit through commercials then I better not go with Youtube TV or Hulu Live (unless I pay the latter $15/mo, which is almost twice the monthly fee for Spectrum's DVR). Sling TV does appear to offer a DVR service I could live with, but they don't offer several channels that I routinely record shows on (Animal Planet, Science and Destination America).
So I went with Directv Now - despite it not having any DVR functionality and a very limited VOD selection - because it has all the channels I want and I get a $25/mo discount for being an AT&T wireless unlimited plan customer, but if that DVR they originally promised would be available in Fall of 2017 (ie - by now) doesn't show up by early 2018 then I guess I'll be putting my Roku Premiere+ on ebay and going back to bad old Spectrum.