Quoted from oilspot:

Idk but I wish they had stayed around . I need a sound speech board for my Firepower. ..

Quoted from acebathound:

A lot has changed in the pinball PCB world in the last 3-4 years. It's a lot more competitive. I'm sure the rest of the pinball products are that way too as prices on machines have gone up and there's more cash flowing into the hobby. People see potential opportunities to make money and "perceived profits." I say perceived, because the profits aren't actually as great as people think.
Subtract material costs and fees, and maybe that $100 sale turns into $70 net profit (before taxes). Now the fun part, subtract 35-45% in taxes from that profit (combined federal, state, local taxes and 15.3% social security/medicare) and you're looking more like $40-45 take-home profit depending on tax brackets you're in. If you had a few hours time into assembling the product, the picture doesn't look near as great as it does from the outside. Sure there's ways to not pay as much in taxes, some that work short-term (inventory fudging) and some that are perfectly acceptable deductions.. but if you're being honest for the most part with inventories, material costs and reporting sales -- taxes hit VERY hard. The constant cycling of new sellers on eBay or in a hobby like this that aren't considering themselves a business and see a larger profit than actually exists, creates the tough competition that makes it hard for anyone actually operating as a business to stick around long-term. Eventually reality sets in, but there's always someone new entering the market without having a handle on all the numbers involved to replace them.
What's changed IMO is manufacturing and ease of creating a storefront / conducting business online and finding wholesale/cheaper importing of items. You can easily prototype 3d models, PCBs, etc much cheaper whereas years ago it would have costs hundreds or thousands of dollars just to order up a small number of units. All of this has allowed more people that otherwise may not have found those sources, tried out an idea or had the technical know-how to create a website/shopping cart to get up and running quick. More competition often means lower pricing (usually what's used to gain attention or market share). If you can't adapt or can't hit the pricing you just watch sales eventually become non-existent.
Some of the people that have been providing the community with products are also getting up there in age. Pinlogic, Two Bit are two that come to mind... those guys were pretty well known years ago. I was surprised to see Two Bit website links broken, but someone told me recently that the business was sold off.
So to sum up, beyond loss of interest, I'd imagine the reason we see people come and go is either age related or the ever changing market conditions.
Just my 2 cents.