4 contributing factors could be: Lifespan, Economics, Hardware Limitations, and Operational Purpose. I'll step through each in turn
If your Precursor race have a typical lifespan of around 1,000 of our years, then a 2 year working lifespan for a device is, proportionally, like having to replace your phone every 2 and a half months. Of course, making the materials durable enough to last 20 years may mean it's hard to make them flimsy enough to also fail within 30 years...
One of the Driving Forces behind today's replaceable upgrade-focussed society ("Buy it, break it, buy a new/better one") is Economics - the companies that make the devices want to be able to sell you a new one, as soon as possible. This is basic Capitalism, and there are examples throughout history of Why.
For example: Are you familiar with the adage/claim that white goods in the 50s would last for 50 years, but in the 90s they only lasted 10? Well, it's true - in the early days, when no one had a fridge, or a washing machine, or a vacuum cleaner, companies sold them in droves. Then they hit market saturation, where everyone had everything, and no one was buying any more. So, they went back to the drawing board, and make the new devices cheaper, and less resilient - they want everything to have a lifespan of 5-10 years, so that one year you need to buy a new dishwasher, the next a tumble-dryer, then a fridge, washing machine, freezer, etc. More money for them every year.
If your precursors are a post-scarcity society, they may have completely different economics - or, they may be expanding fast enough that the market is growing faster than it can reach saturation. This would mean that there was less incentive to make devices that needed replacing regularly, and more incentive to be the "reliable" brand that everyone buys because you only need to do so once.
Are you familiar with Moore's Law? It (roughly) states "The number of Transistors in an Integrated Circuit doubles approximately every 2 years". This has 2 consequences: Electronic devices of a certain computing power can keep shrinking, and Electronic devices of a certain size can keep getting more computationally powerful.
This is an "observational law" - a pattern that is seen, rather than a way the Universe is set up - and the pattern wavers (sometimes it more-than-doubles, sometimes less) but it about evens out. However, every so often there is worry that the law will "break" - components that get too small are more strongly influenced by laws of physics that are "drowned out" in larger components, the cost of researching new technology gets more expensive as the "easy" discoveries are tapped out, et cetera.
Usually, we discover some new trick or manufacturing method or metamaterial that allows us to keep going, but eventually we won't. Wires need to be at least an atom thick for current to flow, with insulation to prevent short-circuits, and so on. If your Precursors have hit their limit, then their technology will reach a stage where obsolescence is a waste, and is dropped.
Obsolescence is, at a basic level, a Consumer thing. If you look at a the goods and devices you find on the High Street, they are designed to be used, and then replaced. But! What if we look elsewhere?
Scientific and Military equipment is generally designed to be rugged and to last a long time. This is because you don't want it to break when you are in the middle of Research or an Operation - and especially if you are in inhospitable conditions miles from Civilisation such as an Undersea Laboratory, Volcanic Caldera, Artic Tundra, or a Vast Desert. A lot of this equipment (especially on the Scientific side) is designed to operate for a long time, without regular maintenance - so it needs a decent Power Source.
You also get emergency "Survival Gear". Nothing pretty, but enough to keep you alive or to call for help when something goes wrong. Possibly spare parts to jury-rig a damaged ship/shuttle. This might even be stored in an outpost for anyone stranded on the planet - like a high-tech Bothy. This is not a situation where you want the gear to have run out of power in the Hundred years or so since anyone last passed by! The technology would be basic, and simple to use. The Precursors may even have sent out automated "seed ships" to build shelters on barely-habitable planets that they have never actually visited, as a "Safety Net" for Explorers and Travellers, like a "Hyperlane-side Assistance" scheme.
(This last point could be compared to an Abacus-using society discovering a cache of mechanical calculators stored for in case our Computers fail, and undergoing a technological revolution based on that - all without realising quite how far ahead of that we really are)
Edit for the "Planned Obsolescence" naysayers: Apple and Samsung have, just this week, been handed fines of €10m and €5m for writing and deploying "software updates" specifically designed to reduce performance of their older phone models as a form of planned obsolescence. In Apple's case, this included reducing Battery lifespan, hence the higher fine.