I got interested in this whole length of engagement and lifestage thing so I went to Wiki. Not definitive, but interesting, and it may serve to explain some of the responses both to the thread and by others hearing of engagements:
"The exact duration of a betrothal varies according to culture and the participantsí needs and wishes. For adults, it may be anywhere from several hours (when the betrothal is incorporated into the wedding day itself) to a period of several years. A year and a day are common in neo-pagan groups today. In the case of child marriage, betrothal might last from infancy until the age of marriage.
The responsibilities and privileges of betrothal vary. In most cultures, the betrothed couple is expected to spend much time together, learning about each other. In some historical cultures (including colonial North America), the betrothal was essentially a trial marriage, with marriage only being required in cases of conception of a child. In almost all cultures there is a loosening of restrictions against physical contact between partners, even in cultures which would normally otherwise have strong prohibitions against it. The betrothal period was also considered to be a preparatory time, in which the groom would build a house, start a business or otherwise prove his readiness to enter adult society.
In medieval Europe, in canon law, a betrothal could be formed by the exchange of vows in the future tense ("I will take you as my wife/husband," instead of "I take you as my wife/husband"), but sexual intercourse consummated the vows, making a binding marriage rather than a betrothal. Although these betrothals could be concluded with only the vows spoken by the couple, they had legal implications: Richard III of England had his older brother's children declared illegitimate on the grounds their father had been betrothed to another woman when he married their mother.
A betrothal is considered to be a 'semi-binding' contract. Normal reasons for invalidation of a betrothal include:
- Revelation of a prior commitment or marriage,
Evidence of infidelity,
Failure to conceive (in 'trial marriage' cultures),
Failure of either party to meet the financial and property stipulations of the betrothal contract.
Normally a betrothal can also be broken at the behest of either party, though some financial penalty (such as forfeit of the bride price) usually will apply."
So historically, the engagement has been a specific life stage, involving the development of a relationship
or the opportunity for the couple to get to know each other better in a socially sanctioned way. However, given that this is no longer necessary in many cases in modern society, I guess people wonder why there is a need for a long engagement given that the purpose of the engagement is now fulfilled in some cases by living together.