Unfortunately, address re-use is a very common practice in Bitcoin, much more common than it needs to be, due to the way many wallets are implemented. Re-using addresses is a heuristic that enables analysts to link individual users to multiple payments with a high degree of certainty (If you use the same address again, it can be assumed you are the same person or entity). Therefore, from a privacy perspective, it is considered critical to keep address re-use as low as possible.