In a nutshell, this is happening because more customers want cheap picture frames than expensive picture frames, it’s that simple. But the reasons for and background to this answer are deeper and more, complicated. From the probable beginnings of approximately 2000 years ago men ( and women ) cut real wood from real tree forests to make the four sticks needed for a picture frame. These ancient picture framers appreciated that wood has a texture and grain which can be sealed, polished and varnished for that attractive and unique appearance, since each section of wood is always lightly different from the others. I addition, solid timber has always had many positive qualities. It’s abundant, durable, tough and can be finished beautifully . Properly cured solid wood is strong ... enough to be used in the building of tunnels, mines, forts, buildings and bridges. Man later learn to air-dry wood and season wood so that it could remain stable and straight enough to make stable sections of wood, as needed in picture frames and photo frames. However, as men cut more and more forests to make more and more furniture and other wood products, the price of wood rose in response to higher demand and lower supply. And as prices of the logs the picture frame mouldings were made from manufacturers started thinking about sourcing cheaper, wood-like, raw materials. That’s when the MDF ( Medium Density Fibreboard) technology was engineered to produce the straight sticks of wood frames are made from. It’s worth noting that the main driver of this manufacturing innovation was, by and large, a straightforward commercial goal to maintain or increase profits by sourcing cheaper raw materials. Interestingly, some manufacturers who changed to, or added, picture framing MDF moulding manufacturing began claiming that this change was due to their corporate policies adopting a friendlier and more responsible environmental awareness. Be that as it may, MDF mouldings and frames became more common and widespread from 2000 onwards. The materials is a composite of fine-particle, recycled wood shavings, fibres, chips and sawdust, is chemically bonded with resins and pressed to be a solid, extrusions. Because of the continuous extrusion process, MDF is manufactured densely and uniformly, without prepotent grains, knots or resin streaks that occur in natural wood and may bleed through primers and paints. It also largely free of the twisting and warping and cupping that can affect real wood when this is subjected to undue or excessive humidity or heat and which may also cause it to shrink and buckle. In fact, in the carpentry and joinery industries working with MDF is often preferred to working with wood since the latter is outperformed, especially in sawing, drilling, plunging, countersinking, screwing, routing and many other machining operations. MDF has a stability is very helpful in avoiding later application defects such as paint cracking. Another consideration is the sourcing as MDF is usually cheaper than solid wood and more easily available in many of the more common widths and thicknesses desired. Further, termites and other insects’ infestations are practically unknown to occur in MDF whereas solid wood, being fully organic, is more vulnerable and often requires expensive protection and treatment . As MDF is manufactured with very fine particles it has no texture or grain and is therefore easier and quicker to paint and as it already has a smooth finish. So far as picture frame moulding manufacturing and finishing is concerned the main benefit is that MDF is less than half the price of comparable wood lengths and it looks the same as real wood picture frames when hung on walls. There is however size limitation to MDF picture frames. Small size photo-frames up to medium size ready-made picture frames are fine in MDF material. Larger picture frames than say, 20”x 30” or 50x75 cms ought still be made from solid wood, rather than MDF because latter, small mouldings might bow and strain or weaken the corners and the V-Nailed joints. As a last remark on this topic, it is has been noted that most shopping strip, retail custom picture framers generally do not use MDF or synthetic mouldings. These custom frame stores tend to stock and offer real wood mouldings only. The main reason for this is that MDF and other “imitation” frames are often perceived by Customers as being cheap and of little value. If custom picture frame store owners were to start using these “inferior” materials they would have great difficulty in justifying and achieving the relatively high cost of custom picture frames and custom picture framing.