I have a 5 year old boy and a 6 year old boy (preschool and 1st grade). My preschooler has regular playdates with a couple of friends.
My 1st grader has not had a playdate all school year. I think that there are a few reasons.
1. He's got different kids in his classroom than Kindergarten (but for one girl) and it takes time to make good friends at school.
2. None of the kids in his classroom live in our immediate neighborhood.
3. EVERYONE is super busy.
4. School gets out at 3:45, so by the time everyone is home and done homework, it's dinner time. Then in our house, bedtime comes next.
5. Our weekends are pretty scared family time. My husband travels a ton during the week, so the weekends are "Daddy Days" and all though occasionally we have friends over (family friends with kids similar ages) we do not generally invite friends over. It's just too busy with swimming, and regular family stuff.
I think that when my kids are older they'll ask for more playdates, but right now I'm fine with things the way they are.