These micro-satellites are not high enough up for them or any debris to remain in orbit for a significant amount of time without station-keeping. Cube-sats will usually only last a few years before de-orbiting due to the very slight atmospheric drag at the height they operate. This is a deliberate decision to avoid the issue you mention (and the various space agencies do co-ordinate on this: see https://www.iadc-online.org/). They also have rules which apply to larger satellites which mean that mean if it does not have a naturally decaying orbit there needs to be a plan to de-orbit it or put it into a 'safe' orbit at end-of-life.