why are god and lord sometimes capitalized?

How these names are presented in the Bible is based on the word used in the original language. The Bible was not originally written in English. The Old Testament was primarily written in Hebrew and the New Testament in Greek.
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In the Old Testament, three Hebrew words are predominantly translated into English as "God." When in the lowercase ("God"), it is the Hebrew word Elohiym (2,346 times) or the Hebrew word El (213 times). When in all capital letters ("GOD"), it is the Hebrew word Yehovih (305 times), which is a variation of the Hebrew word Yehovah (more commonly known as Jehovah). 

Jehovah is rendered as "LORD" (all letters capitalized) 6,510 times. In the Old Testament, this is God's holy, personal name. In the original Hebrew language, it is "YHWH" or "JHVH." (The written Hebrew language only had consonants.)
Traditionally, it was considered taking Jehovah's name in vain (Exodus 20:7) to say or spell out God's proper, holy name, with the exception of the high priests on the Day of Atonement. (Yet today, orthodox Jews omit the vowels, writing the name as "G-d" or "L-rd.") God's divine name is spoken of as the Tetragrammaton, a Greek word meaning "the Name of four letters" (YHWH or JHVH). Where "Lord" appears (lowercase), the Hebrew word is generally Adonai (431 times). Wishing to respect God's name, the Jews would say "Adonai" whenever they encountered the Tetragrammaton in the Old Testament Scriptures.

In the New Testament, the Greek word Theos is predominantly rendered as "God" (1,320 times), and the Greek word Kurios is predominantly used as "Lord" (667 times). The words "God" and "Lord" are capitalized in the King James New Testament when mainly using the Hebrew words Yehovih, or Jehovah. 

Five New Testament verses have "LORD" (all letters capitalized) because they are quoting the original language of Psalm 110:1. (See Matthew 22:44; Mark 12:36; Luke 20:42; and Acts 2:34). The word "LORD" is also capitalized in Revelation 19:16; however, it is not capitalized in The Emphatic Greek Diaglott. The famous scholar Albert Barnes wrote, "There is nothing in the original to denote that this should be distinguished, as it is, by capital letters."
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Many truths are contained within these Hebrew and Greek names, and they are worthy of studied consideration. They reveal different divine attributes and qualities, giving greater insight into both God's person and position.

Earl R. Borders

From the  August 2023 issue of The Gospel Trumpeter