In general, spouses in their 50s and 60s are much more adventurous than previous generations have been, as well as much more independent and comfortable with change. They have fewer rules about everything. They are less judgmental, and more accepting of people who are different from the norm.
It should be no surprise, then, that couples in retirement are becoming less tied to each other, and more interested in parallel play. That model meets our needs for both freedom and involvement and is quickly becoming the system in which many older adults are thriving.