Why Does Wireless Gear Degrade Over Time?

I see no reason why it should degrade (at least for such short period of time as 2 years). I've never experienced degradation with any radio devices. I see 3 possible meaningful answers for now:

1. In fact this can be caused by new neighbour routers being on same channel. You can try to manually change channel and see if that helps.
2. Router configuration is somehow reset to lower power output (many routers have ability to set their power output thru configuration).
3. Same as 2, but premeditated by manufacturer (planned obsolescence).

I asked our sysadmin at work, he also never noticed something wrong with our 2-years old and cheap TP-Link Wi-Fi point. No noticeable signal power degradation at all (we allocate large area, so weak signal would be immediately noticed at far rooms).

Update. We recently upgraded our Wi-Fi network at work, so I had a chance to personally test an 8 years old ZyXel P-334WT EE wireless router which worked 24/7 in our office. I've not noticed any weak signal problem compared to my rather new router.

So in addition to my previous assumptions I could only think of really low quality components, that degrade their quality that fast.

Wifi systems can degrade when they can't communicate with other devices on the same frequency, even with a strong signal on the antenna.

A device may not be able to communicate if it can't correctly share the frequency with other devices. The 802.11 spec requires precise timing in the carrier sense multiple access with collision avoidance algorithm. See https://en.wikipedia.org/wiki/DCF_Interframe_Space and https://en.wikipedia.org/wiki/Distributed_coordination_function

Timing requires a clock, usually a crystal oscillator. These are calibrated for the power source. If the power source degrades or drifts, the oscillator will have more jitter. With too much jitter, the system will not be able to synchronize its transmits and receives with the rest of the devices sharing the frequency, especially at higher data rates with shorter windows.

So what's actually failing when a wifi AP degrades is likely the power supply, which then causes clock jitter, which prevents the device from sending recognizable signals. The power supply can be degrade from overheating (poor ventilation), worn out capacitors, etc.