WOW! You really want to get a new home! How awesome!
Although you are looking for specifics on this particular MLS listing, it is challenging to answer you questions, since there are many scenarios that can effect the sale, building and developing of a real estate transaction.
I am going to para phrase what I hear you asking.
You found a lot in the 19053 zip code, that a builder has building plans for and the builder wants to sell without building the house. You are interested in building a modular/manufactured home on this piece of land and you are not sure WHY this builder would sell without building on the lot.
You can do a few things here.
1st you can call the owner of the land and ask him/ her if they are interested in handling the placement of the home you are interested in and you can mortgage the whole expense at the time of settlement IF the seller is able to handle the financial expense of the upfront transaction costs.
2nd you can ask the seller if he/she is interested in building the home that they have plans for and then sell you the home and land at that time, again IF the seller is able to handle the upfront financial expense of the transaction.
3rd you can buy the land, find your own builder and have that builder place you manufactured home on it after you pay for the land.
To continue to asnwer your latter questions another way,
The builder may not have the money to fund the building of a home at this time and would like to sell the land. BUT he/she has performed the initial tasks with the township and zoning board for a new owner to easily build a home on the lot with their own builder.
When you buy land in Bucks County you are required to keep the lawn maintained according to township requirements, which is usually grass height under 8 in. You are required to keep the land safe of harm to any trespasser who enters your property and paying the taxes for the land. You can visit the http://www.bensalemtwp.org
and contact the zoning commission which will direct you to all required maintenance and ordinances for this particular parcel.
Usually, an interested party will hire a qualified, licensed and insured builder who will handle all the township requirements for building on a lot in the county/township.
I strongly encourage you to contact a Realtor in the Bucks County area who can assist you with all of your questions and can give you the proper direction.
Success in finding your new home,