Lore question about the reaper Cycles.

So, been thinking right about how the Reapers rock up every 55,000 years and wipe out all advanced life. This has happened loads of times, (at least 2 times as the Protheans had another race before them) and likely many more times.

Each of these civilisations became extremely advanced and built great structures and things that are expensive or require rare resources.

My question comes down to resources, with so many cycles of advanced species messing about and building big things, (mass relays and the citadel just to name a few). How is there still plentiful resources for the current cycle to exploit and build things with https://100001.onl/ ? Shouldn't the galaxies supply of ore, eezo and rare elements be running out or atleast there be distinct evidence in the geography of places to support these cycles? Like 55000 years ain't long on a geological timescale.