Loose tea is often cheaper and of better quality in my experience. If you brew tea a lot using a reusable strainer seems like a much better choice. I'm also entirely convinced that these plastic pyramid-shaped bags are pure marketing. Then again, I find Lipton tea absolutely terrible regardless of the shape of the bag.
This is indeed my experience as well. Still, the convenience factor of Lipton tea cannot be understated.
I'm personally willing to bring in my own tea, metal strainers + teaspoon measurement to my workplace for example (hot-water is usually available in most offices). But that's probably too much for a lot of people.
In contrast, you can usually get Lipton Tea from the office supplies, use some paper cups (also office supplies), and get to tea drinking without having to buy the supplies.