Why are the books of knowledge, such as Sahih Al-Bukhari and Sahih Muslim, not reprinted in modern and attractive editions to encourage young people to seek knowledge? And would that be considered a sin or an innovation?

What you aspire to — printing some scholarly books with a quality that keeps pace with modern technologies, while considering the readers' circumstances — is desirable and a door to good deeds for which you will be rewarded. The important thing to consider when printing books, especially heritage books, is that they must be free from errors, which have become numerous in this era.