Why is it so hard?!

This morning we all got up bright & early so we could get over to my parents place by 9.30am.
Simons postie bike has a some problems with its gear box and a WEEK ago my step dad offered to have alook. We thought that was great & appreciate the offer. To have the bike looked at by a professional would cost us alot of money that we don't have. So Dave (step dad) picked up the bike on Sunday last week. He hasn't got around to looking at it. Ok fair enough, he has other things to do. But Friday we stopped in & thought we would ask if & when he thinks he can get to it as its costing us in fuel for Simon to be using the car. So ontop of the normal costs of petrol we now also have the repayments on the bike. It would be ok money wise if Simon was actually using the bike to get to work, saving us the money in petrol for the car.
Anyway, Dave said come around on Sunday anytime after 8.30 -9am & he would have a look at it. He mentioned a wanting to go to a truck show later in the day so I said ok, we will be here nice & early so we can get it out of the way, with plenty of time left to go to the show.
We get there & mum comes out & says "Oh we were just about to go out" . WTF? I said Dave said to come early to do the bike. She said " yeah he said to give you a ring & let you know that he would come for Simon later in the day, but hadn't called yet as she thought we will still be asleep".... Ah yeah of course with 3 little kids we would still be asleep at 9.30 am! I said well we all got up & out the door early because Dave said come early. I was so pissed off that I said fine, come on back in the car & turned to leave. Mum said "Oh no you don't need to leave straight away, just hang around to see what Dave wants to do seems your here". So we go inside & Dave says " We can't hang around, we are going out". No, Sorry, I forgot. Or Sorry I meant to call you. Just " can't hang around we are going out". I told him he said to come early & he just looked at me & said Oh did I? Well we are going to the truck show.
I asked when he wouldbe back & he said sometime late this afternoon.
So I said, fine lets go.
Mum kept saying it was her fault, she should of called earlier etc. But No its not her fault. Dave made a plan with us & then backed out & didn't give a shit about the effort for us to get there early. I said to Simon (in ear shot of mum) that When they get back, just bring your helmet & we will take the bike home & find another way to get it fixed.

I am just pissed off that its taken a week for Dave to make some sort of plan & the he backs out at the last minute. Why is it so hard to get help from family. Why offer if you don't have time or want to do it. Why is it so hard to ring the night before?