To avoid any sampling and handling errors and to get the accurate results.
Explanation:
Large sample size in any experiment increases the accuracy of results.
The large sample size in the experiments of Mendel ruled out the possibility of any error caused by handling and sampling. This increased the accuracy of the statistical calculations. The large sample size prevents the effect of any chance errors on the results.
If he studied a small sample it wouldn't be a representative sample. since he got such a large sample there is a chance most likely all organisms follow the rules of evolution.
