If anything, I believe the opposite is true. Both words in English have the stress on the first syllable.
And usually, a “short vowel” sound in English followed by a hard consonant is typically written in katakana includes a small tsu. Hat, net, back, bag, and neck are written ハット、ネット、バック、バッグ、ネック.
So I still think it’s a mystery why ネクタイdoesn’t have a sokuon.
I took a quick glance at this paper to see if there was anything that could explain the discrepancy between necktie and necklace, and I didn’t find anything, but it’s possible I just missed the relevant section. At the very least, those words don’t appear in the paper as examples.
I expect the difference is the R. It’s voiced, which means it would be nekuresu, while the ku in nekkutai sounds more like nekktai.
That would make some sense. But it’s the opposite: ネックレス and ネクタイ.
@Leebo That’s an interesting study. I certainly didn’t read the whole thing, but beyond phonology, I imagine some of the discrepancies may have to do with what the katakana conventions were when the loanword was imported. This may explain nekutai/nekkuresu.
