I think the IEEE struck a balance between simplicity and ease of implementation and features. I don't think the goal was ever to design a standard that could handle thousands of endpoints on commodity hardware.
For what it is, wifi works great. It falls apart when you try to make it do what it wasn't designed to do. There have been missteps along the way, but overall I think the good outweighs the bad.
Lets not throw the baby out with the bathwater.
Many of them have not been without their failures. GSM had several long-standing security issues, some of which went on uncorrected after disclosure [1]. WEP was designed in the 90s and I believe there are a large number of security/encryption methods designed in the 90s that have since been proven flawed, either in design or implementation (RC4/MD5/SHA1 to name a few) Bluetooth has gone a completely different direction than it's original design and is also not without its failures. But the main difference is, each of the standards you listed was designed for a specific task, and works well in doing what it was designed to do. When you leave that area of designed function, they start to break down.
In relation to the wireless technologies(GSM/HSPA/CDMA/LTE, et al...), their design goal was indeed massive systems with 1000's of clients. They employ various technologies that would generally be cost-prohibitive or otherwise impractical (such as GPS synchronization) in the commodity consumer market. I haven't seen the price tag for an LTE tower site, but I bet it is several orders of magnitude larger than a $120 consumer router. Wifi was never designed to do this.
I agree that wifi is not unique in its success, nor is it unique in its failures. This extends to most entities in general. All have their failures and successes, including IEEE.
On a side note, I have never been that concerned with wifi encryption. The vast majority of wifi access is access to the internet. If you are not securing your data before it leaves your control, the short hop over to the access point is the least of your problems.