Because part of the point in creating another language is that it should be different from your own. Otherwise, why bother doing it at all?
Well, pronunciation conventions are going to occasionally be the same between languages, even coincidentally. Like how vowel sounds and the rolling "r" sound are actually pretty similar between Spanish and Japanese, despite the two languages not being related.
If anything, what's weirder to me, is how all the Orlesians, for example, speak English with French accents, despite only the occasional spattering of Justice Friends-level French into their actual speech. I mean, I get kind of why it was done from a writing perspective, but it's more of a standout than some of the actual "foreign languages" not sounding foreign enough, at least for me.
Anyhow, maybe it is all thanks to Merrill's accent.
I think it is, honestly. I feel like a lot of the Elven language use in the series ended up being a result of the actors just being given "nonsense" words to read without being told what they really mean sometimes, nor any coaching as to the proper pronunciation (there's a really noteworthy occurrence of this in Inquisition, with a certain Elven mission contact in the Hinterlands). Though in a weird way, I think that's appropriate for the Dalish sometimes, since they're just sort of half-reforming a memory of a memory.