Because if the same hardware ID is being used by multiple users, and Steam allows multiple users on one PC without any issues, that's in fact over 100% in total. To colour the example, if everyone surveyed have three accounts in their Steam and they logged in to all three to send results, in total that would be 300.00%.
The total of the reported percentages for many of the categories add up to a lot more than a 100% this month though. For example, Video Card Description: pc adds up to 129.77% this month, when it's usually more or less consistently 100%. The relative distribution is probably correct, but it does make me wonder how much we can actually trust the reported numbers.
Steam's hardware survey for October 2024 reveals not much has changed in the PC gaming landscape. Intel CPUs continue to power most PCs, Nvidia's GeForce RTX xx60 class GPUs are still the most popular and the number of Windows 11 users continue to grow.