+1!
It's not hard to get a dedicated fulfillment service once you've hit a decent size (say ~10k/day). But it's a very intensive sales process with long-term commitments.
They also tend to be both opaque and hard to integrate with other systems. Most use end of day EDI (yes, the 30yr old standard), some of the more "modern" ones have multiple drop times/day.
So major fulfillment providers (not UPS, which doesn't do fulfillment; but FedEx/Rakuten/etc.) are both inappropriate for fast-growing, flexible or seasonal loads, and don't support innovation in customer service for eCommerce companies.
FBA is a much more modern (and extremely successful!) service, but is only cost-effective if you're selling on Amazon. Their 3rd-party, non-branded service is not only prohibitively expensive but feature-light and under-developed.
There's plenty of us, little guys that need logistics/fulfillment and the options just suck. There's a huge space between starting (when you can do it yourself with UPS/equivalent or even standard post) and when you hit a few thousand packages per day (when Fedex and similar is a decent option).
I think that when you reach the thousands of packages per day, you are offered those services, but as a small setup with 'only' hundreds of packages, the only option was to do it manually. We had a simple system to handle orders, inventory, manufacturing... It would have been a breeze to integrate an api with it to print the labels automatically to give the guys actually preparing the packages.
We didn't get a lot of issues that usually pop up when talking ecommerce (scammers, false orders), we didn't even get many returns (I only remember a couple of cases) but we did get a few packages that disappeared in transit with no explanation or, obviously, a refund. The process to report those was horrible, similar to cancelling a mobile phone contract and in most cases we had to simply write-off the package and send a new one to the customer (actually, we are waiting for the resolution of a case when a package worth a few thousand euros was lost, we might actually get back that money).
Another thing that was annoying, although I know it's understandable, is that to start getting discounts they require a volume that, as a new company or sole trader you are simply not going to get. Paying the normal rate for Fedex, for example, makes packages quite expensive when you are talking international (and the fact that I live in an island with a population of less than 10M people doesn't help). We basically kept shipping costs to a minimum by eating into our profit margin. We got less money, but helped improve the sales.