No one outside your union can tell you specifically how or why they bargained a certain way. You should get involved more with your union and ask them these questions instead of posting here. Every union is different and they're obligated to explain these things to any member who asks. If any of it discourages you, then it is up to you to educate other members on why you think that's wrong and help get them organized for the next round of bargaining. A union is only as good as its active members.
If your Canadian union isn't working for you and the above doesn't help, then you file a DFR report with the labour board. Even mentioning DFR (duty of fair representation) should get you service if the union is being adversarial.
Well if you're just reading random CBAs without the context of being a worker within that CBA, there is a lot you're going to miss. Unions are not something you can fully understand from the outside looking in. Generally it's only the executives and officers within a union who have a good idea of how the whole thing works.
Lets use vacation time as an example. If you read my CBA you will find I earn 10 hours of vacation time a month, or three weeks a year. That may seem low, but my employer gives us two weeks paid off when the business shuts down for Christmas. So 40% of my vacation time is not mentioned in the CBA. My employer is also generous with sick days and none of that is part of the CBA, so you can add another week and a half of time off a year. So my CBA says I'm entitled to three weeks off a year but really I end up getting six and a half.