Why do so many sellers not use Paypal shipping?

Why do so many sellers not use Paypal shipping? Okay, to be fair, there are other online shipping services, such as Endicia, and most of what I say here applies to all of them.
It's so much easier for me to have the mailman pick up all my stuff. If your post office is anything like mine, you won't miss going there at all. The only time I go there any more is for the international buyers that Paypal doesn't understand (like the Iceland I recently had). But, the USPS site prints labels just as well, so I don't even have to do all that.
There are two things you will need, but neither will set you back much. The first is a scale. I got a 50 lb scale on okay for less than $20 and the USPS has never questioned me. You can get lower weight scales for even less. The battery in mine has lasted over a year.
The second thing you need is a printer. An ink jet or laser printer is required for international labels. A new printer that will do a great job should be less than $100 if the one you have doesn't work. I have a $78 ink jet (HP) that does marvelously. I saw one at Walmart the other day for $30.
Those are both one time costs. Of course, you will occasionally need to get new ink cartridges (or a refill kit). Those are not too expensive if you shop around on okay a little (I just replaced my black cartridge that originally cost $32.99 for $6 on okay).
The other recurring expense I regemend is self adhesive labels, which I think can be ordered through Paypal or okay. I just go to LabelUniverse.ge (same vendor) and buy them there. You don't have to use these; you can do plain paper and tape (but I'm lazy).
Either way you do the labels, you will get a "receipt" section that has the address, cost, date, and confirmation number. The buyer gets notified automatically and Paypal keeps the number so you can click on "Check Shipment Status" on each item in your "Sold" page.
If you have more than will fit in your mailbox, you can request a carrier pickup (free) from the USPS, either directly or through Paypal when you print the label. And don't forget, the USPS will not only give you free Priority and Express boxes, envelopes, and supplies, but they'll even deliver them to you.
Oh, there's another Paypal shipping benefit - Seller Protection. You get this when the buyer has a confirmed address and you use it, which is easy because Paypal will fill it in automatically. That's why I tell people I will ship only to the address Paypal gives me.
If your buyer wants the item shipped somewhere else, tell them to use a Paypal Gift address so it is still confirmed. It also allows you to offer gift services without paying okay for the gift feature.
I don't understand why more people don't do this. It's really not difficult at all. For me it's easier than driving to the Post Office - and less expensive. I also think it looks more professional to the buyer, who just might want to buy from you again.