Your customers churn no matter what. But… you can retain them for much longer time and generate much more value during their life time cycle.
You need to measure their retention/churn. If you can’t measure it you can’t manage it.
Though measuring the retention by cohorts is not difficult, it is laborious if you don’t have a special tool for it. Here is one, you can use for free. Based on familiar MS Excel. You just copy-paste your data there, press a button and you have your analysis done. Download it here and try by yourself.