Excel allows for the democratization of technology, decreasing the barriers to entry and allowing for easier user experience.

People/teams/companies need different degrees of security, complexity, data, etc to their day-to-day operations. Someone may be interested in fiddling with data without others seeing, others may not want to share certain data broadly (answering your point below). Excel has served as a way to unify these needs for the most part. Some other options available tends to fall on the outer-layers, where excel may not be optimal and someone felt a specialized tool could improve speed/quality/cost.