Why is a score of zero in tennis called love?

Brewer’s Dictionary of Phrase and Fable says that it’s probably derived from phrases like “to play for love” (i.e. to play a game for the love of playing it, and therefore for nothing in the way of stakes.) The Oxford English Dictionary seems to support this view. The word was used in English in card games like whist before it is recorded in connection with tennis.

Some people like to think that “love” is a corruption of the French “l’oeuf” (“the egg”), because the figure zero looks like an egg. But so far as I know, nobody can produce an authentic use of “l’oeuf” in this sense in French.

I noticed that the Shorter Oxford Dictionary abstains from expressing any opinion on this topic. Personally I see no clear link between "playing for love" and scoring nil, and I don't think either of the explanations is well documented.
Yet, that such visual comparisons are not impossible may be illustrated by the Dutch habit of calling a O-O score a "specs score" ("Bril-score".)

When checking in the an older version of the Oxford Dictionary I noticed that already in 1780 the "Gentlemen's Magazine" described the origins of "love" in the meaning of "nil" as unknown. "We are not told how love came to mean nil."

The explanations of (a) "to play for love" and (b) "love" = nil in tennis (love-set; love-game, etc.) are given in immediate succession, but as clearly separate usages of the word "love".

An explanation of love is that the scoring system was copied from the game sphairistike, which was played by British officers in India during the 19th century. That game's scoring system was based on the different gun calibres of the British naval ships. When firing a salute, the ships first fired their 15-pound guns on the main deck, followed by the 30-pound guns of the middle deck, and finally by the 40-pound lower gun deck.

Also, it can be traced to the 17th-century expression "play for love," meaning 'to play without any wager, for nothing'. It is this meaning of 'nothing' that love takes on when used in tennis--and in certain card games, as well as in the occasional British football commentary. The proper way to describe a score of zero to zero is to say love-all.

https://tennispredict.com/why-is-tennis-scored-15-30-40

There is no evidence of its origin, but these are the three most popular theories:

1. derives from the French expression for "the egg" (l'oeuf) because an egg looks like the number zero. This is similar to the origin of the term "duck" in cricket, supposedly from "duck's egg".

2. comes from the Dutch expression iets voor lof doen, which means to do something for praise, implying no monetary stakes.

3. comes from the acceptance that, at the start of any match, when scores are at zero, players still have "love for each other".

https://en.m.wikipedia.org/wiki/Tennis_scoring_system