Sell, extract equity, lower rates I suspect are the primary reasons.  

Granted it is a little harder to extract appreciation than cash flow but not much harder.

Historically the rent appreciation of a purchase 5 years previously, cash flows great 5 years after purchase (assuming no equity extraction). 

hey you know I really don't know but I'd like to know a lot, should I extract all the fund I can using Helock ?

RE investors do this all the time, buy some, keep some, plow some of the gains into building a passive portfolio.You want to continually revalue your holdings, and determine the opportunity cost of keeping a given property vs selling and buying something else (factoring in all the frictional costs, taxes, and time of buying and selling properties).Refinancing using higher appraisals and extracting your cash is nice as well, if you have good credit/income and willing local banks.

Every counter party tries to extract maximum value from their transaction, seller may go under contract at $500k, but if he thinks value has gone up prior to closing, he wants more money, you can sue for $100k and 3 years to win, or pay him an extra $50k at closing.

In addition, it implies that there is no short-term extract of the trapped value; no way to re-use that investment in the near term.

However if I do a BRRRR I can achieve infinite return by extracting all of my investment.

On the other hand, if I tie up your property in exchange for peanuts without the resources or intention to buy your property, I will be able to extract an economic rent from a transaction in which I have no legal or a not unconscionable interest. 

Study up on "arbitrage", also.Here's what one of my mentors does: he uses private money and his corporate credit lines to acquire and fix-up properties, then refinances into a traditional loan to pay off his investors and credit lines as well as extracting part of his profit.