The satellite orbited at 320 km. At that altitude the atmosphere drag is non-negligible, so it had to burn fuel to stay there. So the life was limited by how much fuel it had and that is limited by launch vehicle capabilities. If the launch cost get lower, I imagine refueling might become option, but we are not there yet (except for ISS, but that is different case).
Sort of, Aeolus was a technology demonstrator and it had a intended lifetime of three years, which it surpassed. Other Earth Explorer missions have had similar lifetimes, but many have had much longer... I think since these are all very experimental things getting the up and working to prove the technology is the main thing, how long they make it past that is sort of random.
The laser technology for space-based winds measurement is very difficult to make work in space. The requirements on materials, optics, and power dissipation are daunting. This was a technology demonstrator to show that it had a chance of working and it succeeded.
