- Uncountable nouns
Uncountable nouns are referred to as though they were singular, so you can say this information or that information but not these information or those information, because these and those are only for plural things.
- plurale tantum
Because these are always plural, you have to refer to them with the plural forms, these and those: these trousers or those trousers, not this trousers or that trousers.
- Singular-only nouns
There are very few words in English that are really singular-only. Most of the ones that look singular-only either have the same form in both singular and plural, or they function more like mass nouns. The best example I can think of right now is news, which Merriam-Webster calls "plural in form but singular in construction". It's almost always used as a singular: this news or that news.