Why all the "Re" in titles? There have been quite a number of series whose English titles use peculiar forms of Re. I don't mean normal usages like Rebirth or Requiem. Here's some I chose from an alphabetical listing at MAL:


Re Boot
Re-Kan
Re: Cutie Honey
Re:_Hamatora
Re:Creators
RE:Map
Re:Zero (and several spin-off series)
ReLIFE
Rewrite (although normal, seems to conceptually fit here)
Re:Monster
Tokyo Ghoul:re


It is likely that some of these are just using the prefix "re" as often done in English, to mean either "again" or "concerning". What makes these seem odd to me is the variety of ways they use off-kilter orthography. Is it done as a marketing ploy to attract attention?  Or is there some underlying Japanese concept that maps particularly well to English "Re"?

A Japanese student grows up learning three alphabets (two Japanese and the Latin one) plus Kanji. I wonder sometimes if this variety can lead them to think flexibly in how they choose to build titles in English.
For the meaning of the word "Re:" in the title, depends on the Anime

(there seems to be a lot of explanation in the comment section of your answer).

But the reason on why there's an influx of it being used is the fact that it currently sells when used in a light novel, manga, or anime title.

It's like how in gaming after DayZ was out, there was an influx of zombie survival games.
or if you want an Anime comparison, it's like how after Sword Art Online, "Trapped in another world" anime popped up each season (starting the 'isekai' genre craze).

I'm not saying that everything with the word "Re:" in it is a cash grab, it's not; but it's more of a marketing strategy.

The earliest usage (that I can find) of this is in Re: Cutie Honey (2004) and later Re: Hamatora (2014) which is an OVA, and a second season respectively. The most impactful usage of "Re:" though is in Re:Zero.