Unfortunately, people won't fold just because you think they should. They will often call either because they have the proper number of outs, because they have a big stack and are willing to gamble to knock you out, because they're bored and want to double up or leave, because they think you're bluffing, or simply because they like to gamble.
In case #1 the preflop call with J8 was a bit donkish but post flop he was even with you and in good shape even against a pair. Someone else could have easily check-called with mid pair or flush draw so pushing was a risky move. You rolled the dice and got caught.
Case 2 - you definitely had the odds
to call, but it depends how important the bubble is to you. 30% chance (not knowing his cards) that you'll get knocked out right then, 70% that you'll double up, would you take it? If yes, it was the right move but it's simply not going to work out well every time.
Case 4 may be a good one for an exercise - what hands could he have called after the flop, and how many outs does he really have against you? If it turned out he did have the flush how many do you have?