It is weird and can be disconcerting, but the view count on listings may go down if:
some of the recorded views are by bots - the ebay system filters most of these out as they happen, but there is a daily deeper scan done, which may show up further bot views, which when they are removed may cause a reduction in the views total.
for BIN listings, the page view total only covers views in the previous 30 days, so if a listing has been active for longer than that, the number of new views may reduce as the listing ages, which will cause the views total to shrink.
you can find out more here: https://www.ebay.co.uk/help/default/default/page-views?id=4165
@covertbarracuda