Using "Due to" in this sentence

Question

I think in the sentence below, I shouldn't use "due to" as I start it with "One of the main reasons" but I would like to use "due to" because the reason is just a simple phrase. How can I restate this sentence with "due to"

I may say "this is due to ...", but it is just one reason not the only reason.

As a matter of fact, many native speakers of English have problems with spelling correctly. One of the main reasons for this is due to the complex orthography of English.

Update: I myself find this alternative

Part of the problem is due to the complex orthography of English.

Answer 1

If you write

One of the main reasons for this is due to the complex orthography of English.

You are basically saying the same thing twice, roughly "this is because".

So either you write

[One of the reasons is] the complex orthography.

or

[This is due to] the complex orthography.

Now you want to explicitly say that the orthography is but one reason, so you have to "tone down" the due to by some restricting expression, like

[This is partly due to]...
[This is mainly due to]...
....

---

Overlap with your edit:

Yes, your sugestion works too.