If one is going to the store, isn't one in transit to the store? How is that the same thing as intending or planning to go there?
It isn't the same thing. As always, context is our guide.
1. I was going to the store, but I didn't have time. I didn't go.
By not italicizing "I didn't go," you have indicated that "I didn't go" is not part of the context but your interpretation. What about the ducks, Piscean?
If one is in transit to some place, it is not clear, in a contextual vacuum, what not having enough time means. Consider this:
A: What were you doing at two o'clock this afternoon? If, as I think, you were going to the store, did you by chance stop to see the ducks?
B: I was going to the store, but I didn't have enough time.
In such a highly specialized context, the sentence I have described as semantically anomalous actually makes sense.
It means: I was on my way to the store at two o'clock this afternoon, but I didn't have enough time to stop to see the ducks.
As is clear from that example, not having (enough) time in our example need not mean
I didn't have (enough) time to go to the store.
Meanwhile, consider how little sense it would make to say
?I was going to go to the store, but I didn't have enough time to stop to see the ducks.
I think you will agree that
not having enough time to stop to see the ducks bears no inherent contrastive relationship to
intending to go to the store.
Yet
not having enough time to go to the store manifestly does bear an inherent contrastive relationship to
intending to go to the store.
I am not alone in my feelings about this possible meaning of the past progressive. Quirk et al, for example, say:
(p 210) It [the Progressive aspect] may be used to refer to the future or to the future in the past [my emphasis added]:
Are you going to the meeting (tomorrow?
They were getting married the following spring.
(p 218) Future time in the past [...]
(c) PAST PROGRESSIVE (arrangement predetermined in the past)
I was meeting him in Bordeaux the next day.
Of course, I do not mean to suggest that I deny the possibility of the predetermined-arrangement-in-the-past meaning of the past progressive.
A: Why had you put on your jeans?
B: I was going to the store.
But I contend that this meaning leans heavily on the context as a guide, requiring it to keep the in-the-act-of-doing-something meaning at bay.
Consider the following contrast:
(i) I encountered a lot of traffic while going to the store.
(ii)
?*! I encountered a lot of traffic while going to go to the store.
I find (ii) ungrammatical, but I'll rest content with calling it absolutely ridiculous.
Regarding (i), should you want to say that a predetermined-arrangement-in-the-past meaning is possible? I, for one, find it inconceivable there.