I think the big integrators killed it too
You can blame Microsoft who need to get everyone to follow their new business model of renting stuff (Although I think that their business model always relied on renting software, we just called it "Upgrading").
I think we also should also blame the larger VARs who always saw SBS as a threat to their bottom line - They really didn't want something that supports almost all of the IT requirement of 5-75 users for <$10,000.00 and only costs a few thousand a year in upkeep. There is little scope to gouge the SMB punter with multiple servers and CALS of the normal Windows Server lines.
I used to supply and configure SBS to 50 user or less organizations - We wrote and supplied custom software that could use MS SQL Server, and found that it was cheaper and less hassle than supplying Windows and SQL Server separately. Exchange was a "free bonus".
I am retired now, but have been on the Board of a not-for-profit who had a grant to use public money to replace their ageing 12 computer Windows XP professional peer-to-peer network. The hardware was very unreliable, and the users would occasionally get the Windows licence exceeded message when more than 10 users tried to access the same resource. The business relied on a Microsoft Access database, Excel spreadsheets, Word documents and several users running Outlook who would export their e-mail messages to relevant staff to read. It was dreadful, but worked surprisingly well.
With the lure of public money, a very large local VAR gave a quote. They came back with a design that used a bespoke SQL Server/Sharepoint/Exchange; a SNA; networked high quality printers and 7 Windows servers to hold it all together for an organization of 14 staff and a CEO. The quote was $440,000.00. I told the Board that there must have been a mistake and suggested that they got a revised quotation.
I went on a 12 week trip abroad, and when I came back they had installed a cut-down system using only 4 new servers. They also used repurposed one of the old XP machines that had held the Access database as a Backup Domain Controller. The revised cost was only $218,000.00. This might have been acceptable IF IT HAD WORKED. The Exchange Server was under specced so that it was impossible to reclaim unused space as there was not enough disk space to consolidate the databases, so Exchange would fall over taking the SNA and back up server with it. The down-time was in the order of 3 days a week, and the organization was without e-mail for 16 consecutive days. When the CEO asked why they were having problems, the VAR said that the system was too small and that they should have spent more... After an emergency Board meeting (where I showed that if they had used SBS it would have been very difficult to have spent more that $65,000.00 including software), we managed to get the VAR to upgrade some of the hardware such that the down time was only about 1 day a week. The VAR still wanted about $18,000.00 a year to maintain everything.
I had some health issues and retired from the Board. I found out that they then shared the hardware with a larger government/not-for profit organization, and that the down-time was now OK; but the system still did not do what they wanted.
The last I heard, was that that they were looking at getting rid of it all and replacing it with an OS X Mac Mini Server, 3 MacBook Airs/ MacBook Pros for the CEO and clerical staff and the other users would be given iPads and/or iPhones, so that would be a total spend of less than $25,000.00.