E-commerce category pages are usually the highest commercial-intent pages on the site, and usually the worst performing. Three causes account for most of it.
Faceted navigation eating crawl budget
Every filter combination that generates a crawlable URL multiplies your page count. A category with six filters can generate thousands of near-identical URLs. Search engines spend their crawl allocation on those instead of your actual category pages. Fix it with parameter handling, noindex on filter combinations, and canonical tags pointing back to the clean category URL.
Thin or duplicated copy
A category page with a heading and a product grid gives search engines almost nothing to work with. The fix is not a wall of keyword-stuffed text under the fold — it is genuinely useful content: what distinguishes products in this category, how to choose, what buyers typically ask.
Internal cannibalisation
When ‘running shoes’, ‘mens running shoes’ and ‘running footwear’ all exist as separate categories with overlapping inventory, they compete with each other. Consolidate, or differentiate them clearly and link them deliberately.
Sequence
Crawl controls first — otherwise everything else is invisible. Then consolidate overlapping categories. Then improve the content on what remains. Doing it in the other order wastes most of the effort.