Because real CSV has quoting. The sample above contains "Hopper, Grace" — a single field with a comma inside it. Splitting on commas shifts every subsequent column for that row and corrupts the data silently. RFC 4180 also allows escaped quotes and literal newlines inside quoted fields. This converter uses a proper CSV parser for all of it.
Should I enable number conversion?
Only if you know your data. It is genuinely useful for numeric columns, but it will turn "007" into 7, strip the leading + from a phone number, and reinterpret a value like "1e5" as 100000. Leaving it off keeps everything as strings, which is lossless.
Does delimiter detection handle TSV and semicolons?
Yes. Automatic detection samples the input and picks between comma, tab, semicolon and pipe. Semicolons matter in practice because Excel uses them as the CSV delimiter in locales where the comma is the decimal separator.