Why is radioactive decay only useful for the first 8 half lives of any radioactive substance?

Radioactive decay is most useful for dating and analyzing materials within the first eight half-lives because, after this period, the amount of the original radioactive substance becomes significantly reduced, often to levels that are difficult to measure accurately. Additionally, the remaining isotopes may decay into stable products, making it challenging to distinguish the parent isotope from the daughter products. Beyond this timeframe, the statistical nature of decay leads to greater uncertainty in measurements, limiting its practical applications.