yes it does take a while, some will always run away from you, but others will eventually come and greet you, the best thing is to be as quick as you can picking them up, be confident and go for it,the quicker you are at picking them up the less stressful it is for them.once you have picked them up for cuddles, they usually settle down and love the attention. I have 2 piggies that run away, but still love their cuddle time, it's just instinct for them to run away.
It is such a long process but worth it in the end,
Keep offering them food at the bars, they will eventually come and take it.