They prefer 10-14 hours of light per day. If the plant has already been blooming for a while, this might be natural. The largest and most abundant flowers are early in each bloom cycle. Keep the plant well fed and in the proper conditions. This can be from too much direct sun, not enough fertilizer, or a combination of both.
Violets prefer slightly acidic soil.
Too much water . Be sure to water from beneath the leaves and avoid letting the plant sit in excess water for more than a half hour. When the plant gets really crowded, new growth will be small. Most often it is due to several poor cultural factors. It can also happen when the violet gets way too much light.