These games were designed when the vast majority of PC's were equipped with the Intel 486 or early Pentium chips, and ran under the Windows 98 operating system. They were slow compared to today's computers, but the game's coding was designed to fit with that.
For example, I play MM6 on a computer made in about 2004, which has a Win98 partition. When I right-click on the characters wandering round in New Sorpigal, only about three-quarters of them have names. Also, the goodies hidden in the pews of the chapels in the Silver Helms' two strongholds do not appear. To get all the names and to find all the goodies, I have to play the game on my old laptop, vintaqe about 1999, which still runs under Win98. It runs perfectly on that.