I am trying to understand IPA transcriptions in https://dictionary.cambridge.org/us/ when two words are involved. In particular, their rationale for changing some stresses, compared to the stresses in the independent transcriptions, when the words are put together.
For example, roller skate was transcribed as /ˈroʊ.lɚ skeɪt/. There is a space between "ˈroʊ.lɚ" and "skeɪt", and roller and skate were independently transcribed as /ˈroʊ.lɚ/ and /skeɪt/ respectively. This is intuitive to me: first word + space + second word.
rubber band on the other hand, was transcribed as /ˌrʌb.ɚ ˈbænd/. However, rubber and band were independently transcribed as /ˈrʌb.ɚ/ and /bænd/ respectively.
Finally, safety pin was transcribed as /ˈseɪf.ti ˌpɪn/. However, safety and pin were independently transcribed as /ˈseɪf.ti/ and /pɪn/ respectively.
Why the transcriptions are not always first word + space + second word, where first word and second word are the independent transcriptions, such as in the first example? Why the stresses changed in the transcriptions?