Don't let the tough guys on this site get you down! I think this is a great topic and you are doing a great job as OP.
If you have been selling online for 20 years you were aware of the rising costs affecting sellers as is typical in a capitalist society. From my start on eBay in 2001 to now it was a constant sucking of profits year over year from eBay, PayPal, and all the shipping companies. Mind you, nowadays, shipping companies raise prices an average of 5% every year, year over year. UPS and the likes of them tout all the upgrades to their business model as to why this must be endured by their customer base. They (UPS; Fedex; USPS) have grown into a monopoly similar to a utility company. They are practically working together to ensure fast service and faultless tracking.
It is true that a lost package is really rare nowadays, but those shipping companies claim technological advancements to justify a rise in pricing. I believe the act of raising shipping prices really accelerated around the year, 2015. You can probably find time parallels with cheap Chinese goods infiltrating our economy as the starting point. America welcomed global shipping and got much higher rates nationally because of it. In reality, they were upgrading their global footprint and charging everyone in America for it.
My belief is that we have reached margins that do not allow for lateral movement within the structures that have been laid out via sellers like eBay and Amazon. One may refer to this dynamic as "reaching the end of the road", or late stage capitalism.

