Entertainment Tonight's Youtube channel recently uploaded this 1989 interview with John Williams, where discusses his work on the film...

Very cool find, Paul. Always great to see Williams at the piano. I forgot that the scheduling was so tight on this one; wasn't Broughton attached to do the score at one point?

We've been through that a few times over the years Bill. Broughton has a credit on the trailers and was originally going to score it but I'm pretty sure Williams ended up there because it was testing well and everyone could envision it going to the next level so to speak with him involved. Broughton ended up working on several Hughes productions afterwards so that's always been my theory on what happened. I think they paid him back with those other films as there obviously wasn't any bad feelings involved.

I just believe there was more involved than just scheduling as to how Williams ended up there. No offense to Broughton but that movie doesn't become what it was without Williams' score. Either that or it was truly the happiest scheduling issue of all time

I was with my friend Darren Cavanagh when he interviewed Broughton back in the 90s (we usually co-interviewed but I didn't know too much about Broughton's body of work, so I let Darren handle this one!). Unfortunately, having no tape of the interview, I can only go by memory, but as I recall Broughton didn't say anything about being replaced owing to Williams becoming available (and / or affordable).

One thing Broughton did say, was that he didn't think much of Home Alone as a film. When asked how he felt now that it went on to be a huge hit, his feelings were unchanged: "I still think it is a stupid movie" (or words to that effect)!