Please keep answers on-topic, meaning that they're limited to why the question was closed as off-topic, since that is the issue at hand, and until that is addressed, no other reasons relate to why it was closed.
I can't say why the question was closed as "off topic", flags don't appear in the timelines as far as I can tell, and beyond the mod there were no other votes to close.
Going by RandomBen's comment, "Not Constructive" would have been a better close option:
This question is not a good fit to our Q&A format. We expect answers to generally involve facts, references, or specific expertise; this question will likely solicit opinion, debate, arguments, polling, or extended discussion.
There are similar questions already on here, and I'd have thought that this was a good topic - albeit the question could do with a little tidying (grammar in the title, add the ecommerce and/or payment-gateway to it)
- What payment gateways fit my website?
- Accepting money on a website as payment: when do I move past PayPal?
To be honest, the first one (about options) is probably closest to your request - the answer certainly gives you some things to consider - and so the question might better have been closed as a duplicate of that.