WP site's images will not index, but Joomla's will…

Hi everyone!
Hope you are doing well. I am not super new to WordPress, but new-ish. I have been using Joomla for years and started using WP earlier this year. I have found that no matter what I do, one of my WP sites does not have any images indexed in Google, whereas my Joomla site has plenty of images indexed. I am guessing it is user error of some kind, unless there is a chance the WP template prevents it somehow…

Here is some background:
– I have an image sitemap.
– I use effective names for my images.
– I include title and alt text as well as h x w tags.
– I have a robots.txt file that I believe is appropriate for wanting images crawled.
– One of my other WP sites has been able to get some photos indexed, but not all. That site has only about 8 total images.
– The site I need help with has more than 200 images, and not one is indexed. Something is wrong.
– The site is more than one year old. It started out in Blogger and moved to WP early this summer.

Let me know if there is anything else you need. I am happy to share code as well. I am so grateful for any help you can provide!