This is one case where the exclusion of the word is not because it's regarded as a plural: we have no word
smellie in our lexicon. So it's just that
smellies isn't recognized.
Collins Dictionary lists
smellies as a plural noun meaning "pleasant-smelling products such as perfumes, body lotions, bath salts, etc". It's tagged as British English and informal. Wiktionary has a similar entry, though it also states that
the smellies, in Britain, means cinema enhanced with odours.
The word, in the toiletries sense, is certainly used in British publications. The earliest example I found was in the 1991 novel
Angel Hunt, by Mike Ripley:
We were roughly in the middle of St Christopher's Place, which isn't a 'place' in the French sense, just an alley that cuts between Oxford and Wigmore Streets. It has a fair cross-section of shops selling fashion, books, military models and bathroom smellies.
A more recent example is from the
Manchester Evening News on 6 April this year, which had the headline "Passenger caught with nearly £100,000 of cannabis at Manchester Airport - then told officers they were 'smellies'".
I'll add
smellies as a rare word.