Because of the way the MACD is constructed. The MACD histogram measures the distance between the two moving averages which constitute the MACD. If and when the faster MA moves at a steeper angle than the slower, the distance between the two increases and the histogram bars lengthen. When that angle decreases, the separation decreases and the bars shorten.
Once the instrument finds itself in a sustained trend, the moving averages begin to move at approximately the same rate at approximately the same time. They may even "rope". Therefore, the histogram bars shorten even though the instrument is in a sustained trend.
When one observe the MACD curves - not the histogram - there there is indeed no divergence.
I will go to bed smarter this night , thanks for the observation.
Regards,
" Because of the way the MACD is constructed. The MACD histogram measures the distance between the two moving averages which constitute the MACD. If and when the faster MA moves at a steeper angle than the slower, the distance between the two increases and the histogram bars lengthen. When that angle decreases, the separation decreases and the bars shorten. "