According to Trinitarians who believe Philippians 2:6 says Jesus is God, why did Paul add the word 'form' ('morphe')?

Philippians 2:6 is "Ὃς ἐν μορφῇ Θεοῦ ὑπάρχων οὐχ ἁρπαγμὸν ἡγήσατο τὸ εἶναι ἴσα Θεῷ" "Hos en morphe theou hyparchon ouch harpagmon hegesato to einai isa theo" In his talk Philippians 2: Jesus is not God , Dr. Tom Gaston says (~3 min. mark) > "Had Paul meant to say that Jesus was God, or was a god, he would have > had a very simple way of doing so. That's not a difficult thing to say > in Greek. So the fact that he doesn't use those words makes it very > unlikely that that's what he means." If St. Paul had wanted to say Jesus was God at Philippians 2:6 straightforwardly, he could have said so. Instead, he adds the word 'form', as in 'form of God'. Similarly, as Gaston continues > "Also, had Paul meant to be talking about Jesus' *nature* - saying > that Jesus had the nature of God - again, he would have used other > words. Look at this passage from Galatians 4:8, where Paul talks about > the nature of gods. [...] He uses the Greek word 'phusis' for > 'nature', and again, when you look at that verse for 2 Peter 1:4, it > talks about participating in the divine nature, and again the Greek > word used is 'phusis'. **So had Paul wanted to say Jesus had divine > nature, there are other words he could have used to say that. Instead, > what Paul says is that Jesus was in the form of God. The word he uses > is 'morphe', which is most commonly used in reference to *outward* > appearance, rather than essence or being** [as is done at Mark 16:12]." Why, according to Trinitarians who believe Philippians 2:6 is saying Jesus was God, did Paul add the word 'form' ('morphe')?