How can a worksheet have maximum number of rows?

Worksheets have to have a limit on the amount of rows you have. A computer only has a limited amount of memory, so it cannot be infinite. The vast majority of spreadsheets will not come anywhere close to using them, so you have more than enough. While you can insert extra rows, the amount of rows stay the same and the bottom row is pushed off the spreadsheet. The same applies to the final column. As no data is likely to be there or anywhere near the last row or column, there is no problem in pushing them off. Up to Excel 2003 there were 65536 rows and 256 columns. From versions 2007 on there are 1048576 rows and 16384 columns as modern systems do tend to have more data than the earlier versions were capable of dealing with.