だけに is a grammar pattern that is often translated as 'as might be expected of (A)', 'it's only natural due to (A)', or simply 'because of (A)'. Being a combination of だけ 'just', and に 'to', the literal meaning is 'just in that it's (A)', and is similar to the counterpart phrase in English.
だけに may be used when highlighting either positive or negative results that came about due to (A), and will appear after verbs, い-Adjectives, な-Adjectives that have been followed by な, or nouns.
トムさんは日本語（にほんご）を8年（ねん）勉強（べんきょう）しているだけに、日本語（にほんご）がペラペラだ。
Tom has been studying Japanese for 8 years and as one might expect, he is fluent in Japanese.
このアパートは東京（とうきょう）駅（えき）に近（ちか）いだけに、家賃（やちん）が高（たか）い。
This apartment is very close to Tokyo station, and as one might expect, the rent is expensive.
このアプリは便利（べんり）なだけに、どんどんとユーザーが増（ふ）えてきています。
This application is becoming more and more popular just because it is so useful.
夏（なつ）休（やす）みであるだけに、海水浴場（かいすいよくじょう）には人（ひと）がたくさんいる。
It is summer vacation and as one might expect, there are a lot of people at the beach.
Also,
だけに may be used when highlighting that specifically because of (A), (B) is considered a level above what would usually be expected. This can be in terms of difficulty, emotional reaction, volume, or anything else that is quantifiable.
合格（ごうかく）したと思（おも）っていただけに、不合格（ふごうかく）と知（し）った時（とき）はとてもショックだった。
I was very shocked when I learned that I had been rejected because I thought I had passed.
普段（ふだん）は優（やさ）しいだけに、彼女（かのじょ）が怒（おこ）っている姿（すがた）を見（み）た時（とき）はびっくりしました。
I was surprised to see her angry because she is usually so kind.
Fun-fact - With any of these meanings, the equivalent 'just in that it's (A)' English expression can be utilized as an accurate interpretation, as both it and だけに often just draw the listener's attention to (A), in order to show that (B) is noteworthy because of it.
彼（かれ）は子供（こども）の頃（ころ）からそろばんを習（なら）っているだけに、暗算（あんざん）がとてもうまい。
Just in that he has been learning the abacus since childhood, he is very good at mental math.