ＫＤＤＩは、いろいろな会社のビルやデパートなどでこのサービスを利用してほしいと考えています
KDDI want to use this service in various companies and department stores.
What nuance does adding 考えています bring to this sentence? Why not just say:
ＫＤＤＩは、いろいろな会社のビルやデパートなどでこのサービスを利用してほしいです。
The literal translation of "considering that they want to ..." is obviously clumsy.
「ＫＤＤＩは、いろいろな会社{かいしゃ}のビルやデパートなどでこのサービスを利用{りよう}してほしいと考{かんが}えています。」
Your (it is your own, is it not?) translation is:
"KDDI want to use this service in various companies and department stores."
Before getting to the main part of your question, I must first say that you are not reading the grammar structure of this sentence correctly. To me, this is far more important than the main part of your question.
This is not about a service that KDDI wants to use. Rather, it is a service that KDDI offers.
It says 「（KDDIは）利用してほしい」 and not 「（KDDIは）利用したい」. The difference is huge. Are you following me?
Who does KDDI want to use the service? It is the people at いろいろな会社のビルやデパートなど.
Moving on to your question... Your question actually is a good one.
Adding 「と考えています」 at the end is necessary. That is because ending this sentence with 「ほしいです」 would make KDDI sound really greedy, unrefined, too straightforward, etc. 「考えています」 helps reduce all that in nuance; It balances things out nicely. It does not matter if "thinking" is already included in "wanting".
You will frequently see/hear sentences ending in:
「～～たいと考えています。」 and
「～～たいと思っています。」
Being indirect is a key to well-spoken/written Japanese. (It only makes direct translation somewhat difficult as a drawback.)
「考えています」 could simply be ignored in the translation. You could just say "KDDI would like ~~ to use this service." without using "is thinking" or "thinks".
There are two major problems in your understanding:
してほしい ≠ "want to do"
To tell your own wish to do something, you can just use [verb] + たい (食べたい, 行きたい, 利用したい etc.) してほしい is "want somebody to do", used when who does it is not who wants. Therefore, the original sentence should be translated "KDDI wants them/people to use..." or "KDDI wishes the service to be used..."
ほしい for non-first-person subject
ＫＤＤＩは、いろいろな会社のビルやデパートなどでこのサービスを利用してほしいです。
This sentence doesn't only differ from the first sentence, but is also ungrammatical.
There's a rule: mental adjectives cannot be used as assertive, indicative predicate when the subject is other than I/we. In other words, you can't declare somebody other than you is 眠い ("sleepy"), うれしい ("happy"), かゆい ("itchy") etc. because those are their internal feelings you can't touch (unless you're a telepath).
The word ほしい, despite the English translation "want", is an adjective, that is no exception of this rule. So is たい, maybe you've learned elsewhere that you must reword たい to たがる when it's not your desire. So, if I had to interpret the sentence above, I'd say it means "I want KDDI to use..."
× 彼は……利用してほしいです
× 彼は……利用してほしくないです
○ 彼は……利用してほしがっています ("acts like..., apparently...")
○ 彼は……利用してほしそうです ("looks like...")
○ 彼は……利用してほしいそうです ("says that..., reportedly...")
○ 彼は……利用を望んでいます (verbs are OK)
○ 彼は……利用してほしいですか？ (OK if uncertain)
○ 彼は……利用してほしいと（願って／思って／考えて etc.）います
There are two parts to this phrase, and each must be considered separately.
The verb ending ～たい means that the speaker themselves wants to do the action of the verb.
The verb ending ～てほしい means that the speaker wants someone else to do the action of the verb, usually in some way that is for the speaker, or to the advantage of the speaker.
So in your sample sentence, KDDI doesn't want to use the service themselves -- instead, KDDI wants other people to use the service. This service is probably something that KDDI offers, and management is hoping to get customers from corporate offices and department stores.
This is literally "is thinking about ~". In this context, it's a softener. It's a bit like the difference in English between saying, "I want you to do XX" versus "I was thinking, it'd be nice if you did XX."
Depending on the context, a more idiomatic translation might be:
KDDI management is hoping that people in various locations like corporate office buildings or department stores might use this service.
