"It's quick and easy." This is a short and simple answer. Quick is a great way to describe the speediness of fast food.
"I like how easy and convenient fast food is." Using I like at the beginning will tell the person that it suits you're lifestyle at the current moment in time.
"It's quick and easy."（早くて楽だから）
これはシンプルで短い答えです。"Quick" はファストフードの早さを表すのにピッタリの言葉です。
"I like how easy and convenient fast food is."（ファストフードの簡単で便利なところが好き）
始めに "I like"（私は～が好き）を使うと、それが自分の現在のライフスタイルに合っていることが伝わります。
Both of these answers explain that fast food is easy and convenient as a consumer.
Sometimes sitting down for a long meal is not possible and so a quick burger/sandwich is a more suitable and sometimes affordable choice.
I eat take out because it's easy to get and convenient
When you want to explain that the reason you eat fast food is because it is easy to get and convenient; then you can say it in the following ways:
-It's easy to get and very convenient
-I eat take out because it's easy to get and convenient
ファストフードを食べるのは「手軽で便利だからだ」と説明したいなら、次のように言えます。
-It's easy to get and very convenient（手軽ですごく便利だからです）
-I eat take out because it's easy to get and convenient（ファストフードを食べるのは手軽で便利だからです）
Many people eat fast food as it is easy or simple to get hold of, you don't have to cook it or prepare anything this can be called 'simple and convienient' or 'quick and easy'
簡単ですぐに手に入るのでファーストフードを食べるという人が多いです。調理をしたり何か準備をする必要もありません。これは 'simple and convienient'（簡単で便利）や 'quick and easy'（早くて簡単）と表せます。
"Fast food is convenient and fast to eat."
When expressing that you like to buy fast food you may use this phrase.
"It may be convenient as it is quick to order, buy and eat." This could be useful if someone follows up your statement with " why is it convenient?"
"Fast food is convenient and fast to eat."（ファーストフードは便利で速く食べられるから）
ファーストフードが好きだと伝えるときにこのフレーズが使えます。
もし "why is it convenient?"（どうして便利なの）と聞かれたら、
"It may be convenient as it is quick to order, buy and eat."（素早く注文して買って食べることができるので便利です）
と言えます。
I love fast food because it's readily available and convenient.
If when asked why you eat fast food, you wish to mention that it is because fast food is easy to get and convenient, then you may apply the above statement.
Readily available = Easy to find/obtain
なぜファストフードが好きかと聞かれ、「手軽で便利だから」と答えたいなら、上記のように言えます。
Readily available = すぐに見つかる／手に入る
"It's very easy and convenient"
'convenient' or convenience is describing a task that is easy to do, It can be done with ease and less 'Inconvenience'.
ex. "Having a shop at the end of my street is a real convenience"
"Not having any mobile data on my phone is a real Inconvenience"
"It's very easy and convenient"（すごく簡単で便利です）
= 'convenient' あるいは 'convenience' は、簡単にできることを表します。簡単に不自由（inconvenience）なくできることです。
例：
"Having a shop at the end of my street is a real convenience"（通りの突き当たりにお店があるのはすごく便利です）
"Not having any mobile data on my phone is a real Inconvenience"（携帯にモバイルデータがないのはすごく不便です）
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