All of these were founded by Methodist Christians. John Wesley was an 18th century theologian whom created much of the doctrine and praxis that modern Methodist Christian denominations use. There is today a Methodist group called the Wesleyan Church, but confusingly they actually are not directly associated with most of the schools listed above, because of various splits and mergers between the various different Methodist churches in North America over the past 200 years.

So at one time "Wesleyan" was a commonly used descriptor for Methodist Christian churches and schools, and all of the schools you mentioned either were founded by Methodists or are still officially affiliated with one branch or another of Methodism.

They are named after John Wesley (1703-1791) founder of the Methodist Church, one of the larger Protestant Christian denominations, and were founded by that Church and its followers with 'Wesleyan' in their names in reflectance of their affiliation. Some of these institutions are now secular, but they all would have had their origins as Methodist colleges, and some retain their connections to the Methodist Church.

These institutions all have web pages that detail their history and present associations, if any, such as this one for Ohio Wesleyan: https://www.owu.edu/about/history-traditions/

Source for John Wesley from the United Methodist Church: http://www.umc.org/what-we-believe/john-wesley