Copyrights protect the mark as is, and derivatives of it, but does not protect the brand from look a likes or from new trademarks that would be confusing.

Consider the Pepsi logo:

I could easily draw a circle half red and half blue with a white line straight across, vertically, or diagonally. In fact:

© 2018 A. K. all rights reserved.

There it is my new logo for my cola company called Hep-C (I'm raising awareness). Under copyright law Pepsi could not come after me because the logo is my own creation. I could even call it Pepsi and it would not be a copyright violation as you cannot copyright words. However, Pepsi has better lawyers than that and with my trademark so similar to theirs and the name sounding so similar (and my new name being potentially disparaging to Pepsi) it would likely confuse consumers between what was Pepsi and what was Hep-C thus under trademark law it would be disallowed for commerce.

Now you would have common law trademark protection by virtue of using your mark in commerce, but it would only be for the states in which you used it. Additionally a lack of a registered trademark would disallow you from seeking statutory damages under 15 U.S.C. § 1117.

So, what's the point to make a logo as a trademark?

The general answer is that copyright and trademarks provide different kinds of protection. Speaking very broadly, copyright protects against unauthorized copying and distribution with some fair use exceptions. Trademarks protect a mark from being used by others in a way that might confuse consumers. Additionally, copyright has limited (but long) duration, while trademarks can theoretically be protected indefinitely.

However, i'm going to spend the rest of this answer addressing some misunderstandings.

If something is too simple to create, it cannot be registered as a trademark, it's the same as how copyright works.

This is true for copyright (though a very low bar), but simple things can in fact be trademarked. Trademarks are industry specific, for example, UPS has trademarked the color brown.

Therefore, if my logo (not logotype) can be registered as a trademark, then I have the copyright of my logo.

No, trademarks and copyrights are separate processes. Copyright is in fact inherent, no registration is required (though necessary in the US to get statutory damages).

Only because trademark can be owned by a company not just a person?

At least in common law countries, both trademarks and copyright can be owned by natural persons or companies.

Let's look at this the other way round, say I am starting a new company I do not wish my customers to be confused by having a logo that looks like your logo. But as you are not operating in the same town as me I do not know what your logo looks like or even that you may be expanding into the town I am operating in.

By registering your trademark using a well written description of it I can search the trademark database and find your trademark and hence avoid a lot of confusion for both of our customers.

版權可能會阻止您的徽標未經許可而被複製，包括指向您的產品並做廣告。如果一家商店沒有在其廣告傳單中包含您的產品，那將是一個無恥的舉動，因為您會在徽標上擁有版權聲明，這對於他們來說要獲得所有產品製造商的明確許可才能使用其徽標將是一項艱鉅的工作。

換句話說，版權和商標保護著不同的事物，最特別地意味著對不同用途的許可。

還值得注意的是，特別是版權已經涵蓋了很多內容比最初設計的更多。創建版權後，計算機程序以及音樂和電影（或實際上沒有任何機械的）記錄都不存在。它們被歸類為版權的統治，隨後版權立法變得越來越具有包容性。相比之下，商標法並沒有得到那麼多的擴展，而美國對專利的擴展也涵蓋了設計和軟件方法，這在國際上從未見過。

因此，考慮版權是很自然的事情。作為適用於所有事物的工具，但特別是在您實際上想要廣泛傳播的地方，它包含的默認保護卻是喜憂參半。