When using SORT on a Numeric field, the numbers in Post Meta are stored as LONGTEXT so you need to cast them as numbers first.
CAST( product_page_weight.meta_value AS SIGNED ) DESC
Other Helpful Documentation on Sorting
Sorting DATE Fields Using CAST
When using SORT on a Date/Time field, the numbers in Post Meta are stored as LONGTEXT so you need to cast them as Date & Time Fields first. Typically, they are stored as yyyy-mm-dd hh:mm:ss but if you’re doing date/time math or sorting, you’ll solve a lot of issues by using CAST: CAST( date_time_field.meta_value AS …