Well, I have to say that I don't entirely agree with some of these views. I've had links with the food industry for many years and there's more to this than meets the eye.
The reality is that these pots could be capped with a proper lid for next to nothing. The benefit to the manufacturer is that most people simply can't be bothered to tip any unused contents into an alternative sealable container and those that do will forget when they transferred it within a day or two and bin the contents. Consequently, most people will finish the pot contents on the day of opening. In turn, sales of the product will increase. A well known yogurt manufacturer surveyed 3230 consumers a few years ago about these plastic films and established that consumer behaviour had increased sales by subtly encouraging entire container consumption. That's the reality in this money orientated world but please don't shoot the messenger over this.
Yes, we can all go out and buy lids, but why should we when the manufacturer can provide a reliable, secure and tested lid at fractions of a penny? Regarding the recycling issue, most of these containers disclose that the metal or plastic film cannot be recycled. Plastic lids can be recycled in virtually all cases just like the pot itself. Being careful when taking off the plastic film does not work as the plastic film will not stick to the container a second time as it's thermally applied in the factory. Faffing around writing use by dates on containers is something that's not acceptable to many when the manufacturer can resolve it all very simply and safely by bunging a recyclable plastic lid on the pot.