Y'see, this is where people saying "How hard can it be to make a website" show their IT experience.
Short form, things handling large volumes (and the definition of "large" is very variable) need to be designed right. Things that work well for 10 can start to groan when it comes to 1,000, unless designed with 1,000 in mind. And that assumes you have the right tools in the first place. The last job I was at did a project that was phase 1 for about 100 transactions a month, phase 2 10,000. We told'em ... and they didn't bother to architect for phase 2, and phase 2 runs like a dog. And that's professional IT developers! ::)
The old CSO website was done by a volunteer/volunteers using tools he/they knew. But as the site grew, performance dropped. CSO is purely a voluntary effort, so it's not a case of waving a magic wand (or dropping $10K) for something better. I believe something better is in the works - again, purely voluntarily.