The iPad 1 is literally almost 7 years old, which is an eternity in computers, but even more so in mobile devices. You won't be able to upgrade your device past iOS 5.1.1. Even if it can be argued that maybe it could've gotten one or two more updates, that Apple stopped updating it prematurely, at some point the hardware is literally incapable of running the software. The iPad 1 has long since passed that point. (It received OS updates for two years after release.)
Most apps (at least commonly-used and updated ones) have long since abandoned iOS 5.x as a supported platform. Even Facebook, which has a vested interest in ensuring that the reach of its app is as wide as possible, requires iOS v8 or above. Instagram requires iOS v8 or above. Google Maps requires iOS v7 or above. The list goes on. The hardware simply isn't capable of running modern apps.
Apple has a track record of supporting hardware far longer than its competitors. Most iOS devices receive four years of updates, compared to competitors who ship devices with versions of Android that are outdated at the time the phone is released, and then maybe get one update if it's a particularly well-selling model.
