XLSX is awkward for scripts, databases and import tools that expect plain text. SQLite keeps tables, types and indexes together in one file. XLSX is at home in spreadsheets with formulas, formatting and several sheets; SQLITE is the usual choice for application data in a single portable file.
Each column gets one type chosen from all of its values: a column is numeric only if every non-empty cell is a number, and anything mixed, or a value such as a ZIP code with a leading zero, stays text. Each sheet becomes a table named after it, and a table may have at most 2,000 columns.