Adding on to Tom's response -- I've had DirecTV since 2004, and intend to continue with them for the foreseeable future, but I can think of a number of reasons why they're losing subscribers.
They've basically had two constituencies all along: people in areas where cable is available, where DirecTV has long been sold as a "premium" option; and people in areas where cable isn't available at all.
For that first group:
1. Cable companies have increased their channel offerings and improved their technology over the years, so DirecTV doesn't necessarily have the "premium" advantages they once had. (One big reason I switched from cable to DirecTV in 2004 was to get a DVR that could record two shows at once, which was impossible with cable at the time. I now have a DirecTV DVR that can record five shows at once, but cable's caught up with that in many cases.)
2. Most of those people have high-speed Internet available to them, which makes it easy to "cut the cord" entirely and switch to streaming options.
3. AT&T has attempted to compete with cable companies' TV/Internet/phone bundles by offering DirecTV/Internet/wireless bundles, but AT&T hasn't built out its high-speed Internet network as much as cable companies have. (Last I checked, at my address in the city of Los Angeles, the best AT&T can offer is 6Mbps DSL, so the only usable high-speed Internet option for me is the local cable provider, Spectrum. Yes, I pay two separate bills each month.)
4. DirecTV's price has gone up quite a bit over the years (an inflation calculator tells me inflation is 38.5% since 2004, but my DirecTV bill has gone up well over 100% for a comparable level of service).
5. DirecTV's major exclusive premium sports package, NFL Sunday Ticket, has gotten less valuable over the years with the NFL starting up the RedZone channel for cable subscribers, as well as moving some games off Sundays to other days of the week (most notably, the Thursday night package).
6. DirecTV and cable companies both rely on contracted installers, but it's a lot more "fiddly" to get a DirecTV setup perfected -- if the installer doesn't have the proper level of expertise, it can result in issues like what happened with Tom's friend, where the signal is going out in bad weather a lot more than it should. (On those occasions when it's pouring rain in Southern California, I tend to only get very brief glitches, which are more livable than cable being completely out for a length of time.)
For that second group:
1. As happened in PGage's case, more areas have cable or other options available these days, including Internet options.
2. DirecTV's satellite competitor Dish Network has done a good job of positioning themselves as a less expensive alternative, especially for people who aren't sports fans (they've taken a hard line on negotiating for channel carriage, and one big result is that many sports channels that are on DirecTV are not available on Dish).