The Summer leading into Senior year is crunch time for the non-Power 5 D1s, and D2s and the D3's are reaching out hoping to land some of that talent but recognize they are typically going to have to wait until the Fall admissions process plays out before they get firm commitments. Some kids will commit to D3s now if that is truly their choice, but without sports money and the need to figure out academic money closer to admission time, the D3s will usually wait if they want a kid bad enough.
Your son sounds similar to my 2017 who was getting some interest from the lower D1s and D2s. As others have said, your son needs to keep all of his options open unless he finds that perfect fit of baseball opportunity, academic interest match and financial fit. And it is true, once he mentions there is other interest from a higher level or a strong competitor that he is talking to, it is amazing how much the interest picks up.
And not to be critical, but the reality is the D2 and D3 coaches may be viewing your son as being in that pond for them based on what they have seen. My son finally figured it out and realized the D1 "dream" may be a mirage for kids who will never get to play and just ride the pine. D2 and D3 Coaches will push hard the idea of being one of the key players for their team (maybe as early as Freshman year) versus what the opportunity would be at the D1s. One D3 coach seriously said something to the effect that the D1 key players who will be starting/playing were locked up back in their Sophomore and early Junior years. He was probably right and it definitely had my son thinking. He is now much happier and much better off in D2 than some of his fellow league players who signed up with lower level D1 teams and are already back in JUCO looking for another opportunity. They wound up in the wrong pond.
Good luck--this is the most exciting time for you and your son. From now till the end of the year it will be anxiously waiting to hear back from coaches and planning visits.