I would guess it's not exactly - well not intentionally - controlling or manipulative, but it's an anxiety based avoidance.
All communication is not the same, OP. Think about it and you will know this. Asking someone what they had for tea last night is very different from asking someone if they could shower more frequently. The latter you would put off, rehearse, choose your words carefully etc because of the potential reaction you would get. This concept is called "communication load". Some communication tasks are low communication load, and some are high. Generally rote speech, responding to short questions, expert speech (talking about something you know a lot about), are lower communication load. Risky speech, having a guess, hypothesising, exposing speech, these are high communication load.
People who struggle with communication load often manage much better in their best space, ie with their partner, than with anyone else. But might avoid making calls to book a plumber etc, getting their partner to do it and being a bit arsey. Importantly they probably don't quite understand themselves why it feels so hard as the pattern of avoidance is usually entrenched from early childhood and being challenged on it feels "unsafe" - hence disproportionate response.
Announcing a pregnancy (or a marriage, or serious illness, or house move etc) is a very high communication load task, because it is likely to generate a significant reaction that the person feels like they might not be quite able to handle (again, all this is subconscious. It's the person's anxiety protecting itself). I strongly suspect that is why he's avoiding doing it. At one level he knows it's irrational, but it just feels difficult.
I would take the position that the longer he leaves it, the bigger deal it is likely to be. If he announces now it could be spun that it's because you were waiting for test results etc. No need to mention your side has known for months. If he waits much longer he will have people's dismay and upset that it's been concealed and made weird to deal with. This is the tragic thing about anxious avoidant communication - it often actually causes the feared big response.
Could you suggest that he, or both of you, make an initial low key announcement in family WhatsApp group along the lines of "after getting the all clear from various tests, we are really happy to say we are having a baby due in October :) ". Sometimes the desire for insta moments, dramatic filmed announcements etc piles on more pressure of expectation.
Most people with this type of communication are autistic or have the remnants of a communication disorder such as selective mutism stretching a long shadow into their ability to communicate into adulthood.
Does any of this resonate at all?